-
Notifications
You must be signed in to change notification settings - Fork 3
/
Top-Interview-Questions.html
5732 lines (5413 loc) · 804 KB
/
Top-Interview-Questions.html
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
<!DOCTYPE html>
<!-- saved from url=(0098)file:///private/var/folders/30/cmv9c_5j3mq_kthx63sb1t5c0000gn/T/mume202329-17166-6dqij5.n3z44.html -->
<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Top-Interview-Questions</title>
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<link rel="stylesheet" href="./Top-Interview-Questions_files/katex.min.css">
<style>
/**
* prism.js Github theme based on GitHub's theme.
* @author Sam Clarke
*/
code[class*="language-"],
pre[class*="language-"] {
color: #333;
background: none;
font-family: Consolas, "Liberation Mono", Menlo, Courier, monospace;
text-align: left;
white-space: pre;
word-spacing: normal;
word-break: normal;
word-wrap: normal;
line-height: 1.4;
-moz-tab-size: 8;
-o-tab-size: 8;
tab-size: 8;
-webkit-hyphens: none;
-moz-hyphens: none;
-ms-hyphens: none;
hyphens: none;
}
/* Code blocks */
pre[class*="language-"] {
padding: .8em;
overflow: auto;
/* border: 1px solid #ddd; */
border-radius: 3px;
/* background: #fff; */
background: #f5f5f5;
}
/* Inline code */
:not(pre) > code[class*="language-"] {
padding: .1em;
border-radius: .3em;
white-space: normal;
background: #f5f5f5;
}
.token.comment,
.token.blockquote {
color: #969896;
}
.token.cdata {
color: #183691;
}
.token.doctype,
.token.punctuation,
.token.variable,
.token.macro.property {
color: #333;
}
.token.operator,
.token.important,
.token.keyword,
.token.rule,
.token.builtin {
color: #a71d5d;
}
.token.string,
.token.url,
.token.regex,
.token.attr-value {
color: #183691;
}
.token.property,
.token.number,
.token.boolean,
.token.entity,
.token.atrule,
.token.constant,
.token.symbol,
.token.command,
.token.code {
color: #0086b3;
}
.token.tag,
.token.selector,
.token.prolog {
color: #63a35c;
}
.token.function,
.token.namespace,
.token.pseudo-element,
.token.class,
.token.class-name,
.token.pseudo-class,
.token.id,
.token.url-reference .token.variable,
.token.attr-name {
color: #795da3;
}
.token.entity {
cursor: help;
}
.token.title,
.token.title .token.punctuation {
font-weight: bold;
color: #1d3e81;
}
.token.list {
color: #ed6a43;
}
.token.inserted {
background-color: #eaffea;
color: #55a532;
}
.token.deleted {
background-color: #ffecec;
color: #bd2c00;
}
.token.bold {
font-weight: bold;
}
.token.italic {
font-style: italic;
}
/* JSON */
.language-json .token.property {
color: #183691;
}
.language-markup .token.tag .token.punctuation {
color: #333;
}
/* CSS */
code.language-css,
.language-css .token.function {
color: #0086b3;
}
/* YAML */
.language-yaml .token.atrule {
color: #63a35c;
}
code.language-yaml {
color: #183691;
}
/* Ruby */
.language-ruby .token.function {
color: #333;
}
/* Markdown */
.language-markdown .token.url {
color: #795da3;
}
/* Makefile */
.language-makefile .token.symbol {
color: #795da3;
}
.language-makefile .token.variable {
color: #183691;
}
.language-makefile .token.builtin {
color: #0086b3;
}
/* Bash */
.language-bash .token.keyword {
color: #0086b3;
}
/* highlight */
pre[data-line] {
position: relative;
padding: 1em 0 1em 3em;
}
pre[data-line] .line-highlight-wrapper {
position: absolute;
top: 0;
left: 0;
background-color: transparent;
display: block;
width: 100%;
}
pre[data-line] .line-highlight {
position: absolute;
left: 0;
right: 0;
padding: inherit 0;
margin-top: 1em;
background: hsla(24, 20%, 50%,.08);
background: linear-gradient(to right, hsla(24, 20%, 50%,.1) 70%, hsla(24, 20%, 50%,0));
pointer-events: none;
line-height: inherit;
white-space: pre;
}
pre[data-line] .line-highlight:before,
pre[data-line] .line-highlight[data-end]:after {
content: attr(data-start);
position: absolute;
top: .4em;
left: .6em;
min-width: 1em;
padding: 0 .5em;
background-color: hsla(24, 20%, 50%,.4);
color: hsl(24, 20%, 95%);
font: bold 65%/1.5 sans-serif;
text-align: center;
vertical-align: .3em;
border-radius: 999px;
text-shadow: none;
box-shadow: 0 1px white;
}
pre[data-line] .line-highlight[data-end]:after {
content: attr(data-end);
top: auto;
bottom: .4em;
}html body{font-family:"Helvetica Neue",Helvetica,"Segoe UI",Arial,freesans,sans-serif;font-size:16px;line-height:1.6;color:#333;background-color:#fff;overflow:initial;box-sizing:border-box;word-wrap:break-word}html body>:first-child{margin-top:0}html body h1,html body h2,html body h3,html body h4,html body h5,html body h6{line-height:1.2;margin-top:1em;margin-bottom:16px;color:#000}html body h1{font-size:2.25em;font-weight:300;padding-bottom:.3em}html body h2{font-size:1.75em;font-weight:400;padding-bottom:.3em}html body h3{font-size:1.5em;font-weight:500}html body h4{font-size:1.25em;font-weight:600}html body h5{font-size:1.1em;font-weight:600}html body h6{font-size:1em;font-weight:600}html body h1,html body h2,html body h3,html body h4,html body h5{font-weight:600}html body h5{font-size:1em}html body h6{color:#5c5c5c}html body strong{color:#000}html body del{color:#5c5c5c}html body a:not([href]){color:inherit;text-decoration:none}html body a{color:#08c;text-decoration:none}html body a:hover{color:#00a3f5;text-decoration:none}html body img{max-width:100%}html body>p{margin-top:0;margin-bottom:16px;word-wrap:break-word}html body>ul,html body>ol{margin-bottom:16px}html body ul,html body ol{padding-left:2em}html body ul.no-list,html body ol.no-list{padding:0;list-style-type:none}html body ul ul,html body ul ol,html body ol ol,html body ol ul{margin-top:0;margin-bottom:0}html body li{margin-bottom:0}html body li.task-list-item{list-style:none}html body li>p{margin-top:0;margin-bottom:0}html body .task-list-item-checkbox{margin:0 .2em .25em -1.8em;vertical-align:middle}html body .task-list-item-checkbox:hover{cursor:pointer}html body blockquote{margin:16px 0;font-size:inherit;padding:0 15px;color:#5c5c5c;background-color:#f0f0f0;border-left:4px solid #d6d6d6}html body blockquote>:first-child{margin-top:0}html body blockquote>:last-child{margin-bottom:0}html body hr{height:4px;margin:32px 0;background-color:#d6d6d6;border:0 none}html body table{margin:10px 0 15px 0;border-collapse:collapse;border-spacing:0;display:block;width:100%;overflow:auto;word-break:normal;word-break:keep-all}html body table th{font-weight:bold;color:#000}html body table td,html body table th{border:1px solid #d6d6d6;padding:6px 13px}html body dl{padding:0}html body dl dt{padding:0;margin-top:16px;font-size:1em;font-style:italic;font-weight:bold}html body dl dd{padding:0 16px;margin-bottom:16px}html body code{font-family:Menlo,Monaco,Consolas,'Courier New',monospace;font-size:.85em !important;color:#000;background-color:#f0f0f0;border-radius:3px;padding:.2em 0}html body code::before,html body code::after{letter-spacing:-0.2em;content:"\00a0"}html body pre>code{padding:0;margin:0;font-size:.85em !important;word-break:normal;white-space:pre;background:transparent;border:0}html body .highlight{margin-bottom:16px}html body .highlight pre,html body pre{padding:1em;overflow:auto;font-size:.85em !important;line-height:1.45;border:#d6d6d6;border-radius:3px}html body .highlight pre{margin-bottom:0;word-break:normal}html body pre code,html body pre tt{display:inline;max-width:initial;padding:0;margin:0;overflow:initial;line-height:inherit;word-wrap:normal;background-color:transparent;border:0}html body pre code:before,html body pre tt:before,html body pre code:after,html body pre tt:after{content:normal}html body p,html body blockquote,html body ul,html body ol,html body dl,html body pre{margin-top:0;margin-bottom:16px}html body kbd{color:#000;border:1px solid #d6d6d6;border-bottom:2px solid #c7c7c7;padding:2px 4px;background-color:#f0f0f0;border-radius:3px}@media print{html body{background-color:#fff}html body h1,html body h2,html body h3,html body h4,html body h5,html body h6{color:#000;page-break-after:avoid}html body blockquote{color:#5c5c5c}html body pre{page-break-inside:avoid}html body table{display:table}html body img{display:block;max-width:100%;max-height:100%}html body pre,html body code{word-wrap:break-word;white-space:pre}}.markdown-preview{width:100%;height:100%;box-sizing:border-box}.markdown-preview .pagebreak,.markdown-preview .newpage{page-break-before:always}.markdown-preview pre.line-numbers{position:relative;padding-left:3.8em;counter-reset:linenumber}.markdown-preview pre.line-numbers>code{position:relative}.markdown-preview pre.line-numbers .line-numbers-rows{position:absolute;pointer-events:none;top:1em;font-size:100%;left:0;width:3em;letter-spacing:-1px;border-right:1px solid #999;-webkit-user-select:none;-moz-user-select:none;-ms-user-select:none;user-select:none}.markdown-preview pre.line-numbers .line-numbers-rows>span{pointer-events:none;display:block;counter-increment:linenumber}.markdown-preview pre.line-numbers .line-numbers-rows>span:before{content:counter(linenumber);color:#999;display:block;padding-right:.8em;text-align:right}.markdown-preview .mathjax-exps .MathJax_Display{text-align:center !important}.markdown-preview:not([for="preview"]) .code-chunk .btn-group{display:none}.markdown-preview:not([for="preview"]) .code-chunk .status{display:none}.markdown-preview:not([for="preview"]) .code-chunk .output-div{margin-bottom:16px}.scrollbar-style::-webkit-scrollbar{width:8px}.scrollbar-style::-webkit-scrollbar-track{border-radius:10px;background-color:transparent}.scrollbar-style::-webkit-scrollbar-thumb{border-radius:5px;background-color:rgba(150,150,150,0.66);border:4px solid rgba(150,150,150,0.66);background-clip:content-box}html body[for="html-export"]:not([data-presentation-mode]){position:relative;width:100%;height:100%;top:0;left:0;margin:0;padding:0;overflow:auto}html body[for="html-export"]:not([data-presentation-mode]) .markdown-preview{position:relative;top:0}@media screen and (min-width:914px){html body[for="html-export"]:not([data-presentation-mode]) .markdown-preview{padding:2em calc(50% - 457px + 2em)}}@media screen and (max-width:914px){html body[for="html-export"]:not([data-presentation-mode]) .markdown-preview{padding:2em}}@media screen and (max-width:450px){html body[for="html-export"]:not([data-presentation-mode]) .markdown-preview{font-size:14px !important;padding:1em}}@media print{html body[for="html-export"]:not([data-presentation-mode]) #sidebar-toc-btn{display:none}}html body[for="html-export"]:not([data-presentation-mode]) #sidebar-toc-btn{position:fixed;bottom:8px;left:8px;font-size:28px;cursor:pointer;color:inherit;z-index:99;width:32px;text-align:center;opacity:.4}html body[for="html-export"]:not([data-presentation-mode])[html-show-sidebar-toc] #sidebar-toc-btn{opacity:1}html body[for="html-export"]:not([data-presentation-mode])[html-show-sidebar-toc] .md-sidebar-toc{position:fixed;top:0;left:0;width:300px;height:100%;padding:32px 0 48px 0;font-size:14px;box-shadow:0 0 4px rgba(150,150,150,0.33);box-sizing:border-box;overflow:auto;background-color:inherit}html body[for="html-export"]:not([data-presentation-mode])[html-show-sidebar-toc] .md-sidebar-toc::-webkit-scrollbar{width:8px}html body[for="html-export"]:not([data-presentation-mode])[html-show-sidebar-toc] .md-sidebar-toc::-webkit-scrollbar-track{border-radius:10px;background-color:transparent}html body[for="html-export"]:not([data-presentation-mode])[html-show-sidebar-toc] .md-sidebar-toc::-webkit-scrollbar-thumb{border-radius:5px;background-color:rgba(150,150,150,0.66);border:4px solid rgba(150,150,150,0.66);background-clip:content-box}html body[for="html-export"]:not([data-presentation-mode])[html-show-sidebar-toc] .md-sidebar-toc a{text-decoration:none}html body[for="html-export"]:not([data-presentation-mode])[html-show-sidebar-toc] .md-sidebar-toc ul{padding:0 1.6em;margin-top:.8em}html body[for="html-export"]:not([data-presentation-mode])[html-show-sidebar-toc] .md-sidebar-toc li{margin-bottom:.8em}html body[for="html-export"]:not([data-presentation-mode])[html-show-sidebar-toc] .md-sidebar-toc ul{list-style-type:none}html body[for="html-export"]:not([data-presentation-mode])[html-show-sidebar-toc] .markdown-preview{left:300px;width:calc(100% - 300px);padding:2em calc(50% - 457px - 150px);margin:0;box-sizing:border-box}@media screen and (max-width:1274px){html body[for="html-export"]:not([data-presentation-mode])[html-show-sidebar-toc] .markdown-preview{padding:2em}}@media screen and (max-width:450px){html body[for="html-export"]:not([data-presentation-mode])[html-show-sidebar-toc] .markdown-preview{width:100%}}html body[for="html-export"]:not([data-presentation-mode]):not([html-show-sidebar-toc]) .markdown-preview{left:50%;transform:translateX(-50%)}html body[for="html-export"]:not([data-presentation-mode]):not([html-show-sidebar-toc]) .md-sidebar-toc{display:none}
/* Please visit the URL below for more information: */
/* https://shd101wyy.github.io/markdown-preview-enhanced/#/customize-css */
.markdown-preview.markdown-preview {
font-size: small;
}
</style>
</head>
<body for="html-export">
<div class="mume markdown-preview ">
<h1 class="mume-header" id="1-%E4%B8%A4%E6%95%B0%E4%B9%8B%E5%92%8C">1. 两数之和</h1>
<p>给定一个整数数组 nums 和一个整数目标值 target，请你在该数组中找出 和为目标值 target 的那 两个 整数，并返回它们的数组下标。</p>
<p>你可以假设每种输入只会对应一个答案。但是，数组中同一个元素在答案里不能重复出现。</p>
<p>你可以按任意顺序返回答案。</p>
<pre data-role="codeBlock" data-info="cpp" class="language-cpp"><span class="token keyword keyword-class">class</span> <span class="token class-name">Solution</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-public">public</span><span class="token operator">:</span>
vector<span class="token operator"><</span><span class="token keyword keyword-int">int</span><span class="token operator">></span> <span class="token function">twoSum</span><span class="token punctuation">(</span>vector<span class="token operator"><</span><span class="token keyword keyword-int">int</span><span class="token operator">></span><span class="token operator">&</span> nums<span class="token punctuation">,</span> <span class="token keyword keyword-int">int</span> target<span class="token punctuation">)</span> <span class="token punctuation">{</span>
std<span class="token double-colon punctuation">::</span>unordered_map<span class="token operator"><</span><span class="token keyword keyword-int">int</span><span class="token punctuation">,</span> <span class="token keyword keyword-int">int</span><span class="token operator">></span> mp<span class="token punctuation">;</span>
<span class="token keyword keyword-for">for</span> <span class="token punctuation">(</span><span class="token keyword keyword-int">int</span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">,</span> j<span class="token punctuation">;</span> i <span class="token operator"><</span> nums<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token operator">++</span>i<span class="token punctuation">)</span> <span class="token punctuation">{</span>
j <span class="token operator">=</span> target <span class="token operator">-</span> nums<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">;</span>
<span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>mp<span class="token punctuation">.</span><span class="token function">find</span><span class="token punctuation">(</span>j<span class="token punctuation">)</span> <span class="token operator">!=</span> mp<span class="token punctuation">.</span><span class="token function">end</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-return">return</span> <span class="token punctuation">{</span> mp<span class="token punctuation">[</span>j<span class="token punctuation">]</span><span class="token punctuation">,</span> i <span class="token punctuation">}</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span> <span class="token keyword keyword-else">else</span> <span class="token punctuation">{</span>
mp<span class="token punctuation">[</span>nums<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">]</span> <span class="token operator">=</span> i<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span class="token keyword keyword-return">return</span> <span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</pre><ul>
<li>空间复杂度： O(n)</li>
<li>时间复杂度： O(n)</li>
<li>解法：</li>
<li>标签： <code>数组</code>, <code>哈希表</code></li>
<li>难度： 简单</li>
</ul>
<h1 class="mume-header" id="2-%E4%B8%A4%E6%95%B0%E7%9B%B8%E5%8A%A0">2. 两数相加</h1>
<p>给你两个 非空 的链表，表示两个非负的整数。它们每位数字都是按照 逆序 的方式存储的，并且每个节点只能存储 一位 数字。</p>
<p>请你将两个数相加，并以相同形式返回一个表示和的链表。</p>
<p>你可以假设除了数字 0 之外，这两个数都不会以 0 开头。</p>
<pre data-role="codeBlock" data-info="cpp" class="language-cpp"><span class="token comment">/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode() : val(0), next(nullptr) {}
* ListNode(int x) : val(x), next(nullptr) {}
* ListNode(int x, ListNode *next) : val(x), next(next) {}
* };
*/</span>
<span class="token keyword keyword-class">class</span> <span class="token class-name">Solution</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-public">public</span><span class="token operator">:</span>
ListNode<span class="token operator">*</span> <span class="token function">addTwoNumbers</span><span class="token punctuation">(</span>ListNode<span class="token operator">*</span> l1<span class="token punctuation">,</span> ListNode<span class="token operator">*</span> l2<span class="token punctuation">)</span> <span class="token punctuation">{</span>
ListNode<span class="token operator">*</span> res <span class="token operator">=</span> <span class="token keyword keyword-new">new</span> <span class="token function">ListNode</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
ListNode<span class="token operator">*</span> ptr <span class="token operator">=</span> res<span class="token punctuation">;</span>
<span class="token keyword keyword-int">int</span> isCarry <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">,</span> sm <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span>
<span class="token comment">// l1 and l2 step</span>
<span class="token keyword keyword-while">while</span> <span class="token punctuation">(</span>l1 <span class="token operator">!=</span> <span class="token constant">NULL</span> <span class="token operator">&&</span> l2 <span class="token operator">!=</span> <span class="token constant">NULL</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
sm <span class="token operator">=</span> l1<span class="token operator">-></span>val <span class="token operator">+</span> l2<span class="token operator">-></span>val <span class="token operator">+</span> isCarry<span class="token punctuation">;</span>
isCarry <span class="token operator">=</span> sm <span class="token operator">>=</span> <span class="token number">10</span><span class="token punctuation">;</span>
ptr<span class="token operator">-></span>next <span class="token operator">=</span> <span class="token keyword keyword-new">new</span> <span class="token function">ListNode</span><span class="token punctuation">(</span>sm <span class="token operator">%</span> <span class="token number">10</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
ptr <span class="token operator">=</span> ptr<span class="token operator">-></span>next<span class="token punctuation">;</span>
l1 <span class="token operator">=</span> l1<span class="token operator">-></span>next<span class="token punctuation">;</span>
l2 <span class="token operator">=</span> l2<span class="token operator">-></span>next<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token comment">// l1 or l2 step</span>
l1 <span class="token operator">=</span> l1 <span class="token operator">!=</span> <span class="token constant">NULL</span> <span class="token operator">?</span> l1 <span class="token operator">:</span> l2<span class="token punctuation">;</span>
<span class="token keyword keyword-while">while</span> <span class="token punctuation">(</span>l1 <span class="token operator">!=</span> <span class="token constant">NULL</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
sm <span class="token operator">=</span> l1<span class="token operator">-></span>val <span class="token operator">+</span> isCarry<span class="token punctuation">;</span>
isCarry <span class="token operator">=</span> sm <span class="token operator">>=</span> <span class="token number">10</span><span class="token punctuation">;</span>
ptr<span class="token operator">-></span>next <span class="token operator">=</span> <span class="token keyword keyword-new">new</span> <span class="token function">ListNode</span><span class="token punctuation">(</span>sm <span class="token operator">%</span> <span class="token number">10</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
ptr <span class="token operator">=</span> ptr<span class="token operator">-></span>next<span class="token punctuation">;</span>
l1 <span class="token operator">=</span> l1<span class="token operator">-></span>next<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token comment">// last isCarry = 1</span>
<span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>isCarry<span class="token punctuation">)</span> <span class="token punctuation">{</span>
ptr<span class="token operator">-></span>next <span class="token operator">=</span> <span class="token keyword keyword-new">new</span> <span class="token function">ListNode</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword keyword-return">return</span> res<span class="token operator">-></span>next<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</pre><ul>
<li>空间复杂度： O(n)</li>
<li>时间复杂度： O(n)</li>
<li>解法：</li>
<li>标签： <code>递归</code>, <code>链表</code>, <code>数学</code></li>
<li>难度： 中等</li>
</ul>
<h1 class="mume-header" id="3-%E6%97%A0%E9%87%8D%E5%A4%8D%E5%AD%97%E7%AC%A6%E7%9A%84%E6%9C%80%E9%95%BF%E5%AD%90%E4%B8%B2">3. 无重复字符的最长子串</h1>
<p>给定一个字符串，请你找出其中不含有重复字符的 最长子串 的长度。</p>
<pre data-role="codeBlock" data-info="cpp" class="language-cpp"><span class="token keyword keyword-class">class</span> <span class="token class-name">Solution</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-public">public</span><span class="token operator">:</span>
<span class="token keyword keyword-int">int</span> <span class="token function">lengthOfLongestSubstring</span><span class="token punctuation">(</span>string s<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-int">int</span> res <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span>
std<span class="token double-colon punctuation">::</span>unordered_map<span class="token operator"><</span><span class="token keyword keyword-char">char</span><span class="token punctuation">,</span> <span class="token keyword keyword-int">int</span><span class="token operator">></span> mp<span class="token punctuation">;</span>
<span class="token keyword keyword-int">int</span> start <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span>
<span class="token keyword keyword-for">for</span> <span class="token punctuation">(</span><span class="token keyword keyword-int">int</span> end <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> end <span class="token operator"><</span> s<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token operator">++</span>end<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>mp<span class="token punctuation">.</span><span class="token function">find</span><span class="token punctuation">(</span>s<span class="token punctuation">[</span>end<span class="token punctuation">]</span><span class="token punctuation">)</span> <span class="token operator">==</span> mp<span class="token punctuation">.</span><span class="token function">end</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
mp<span class="token punctuation">[</span>s<span class="token punctuation">[</span>end<span class="token punctuation">]</span><span class="token punctuation">]</span> <span class="token operator">=</span> end<span class="token punctuation">;</span>
<span class="token punctuation">}</span> <span class="token keyword keyword-else">else</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-int">int</span> tmp <span class="token operator">=</span> mp<span class="token punctuation">[</span>s<span class="token punctuation">[</span>end<span class="token punctuation">]</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
<span class="token keyword keyword-for">for</span> <span class="token punctuation">(</span><span class="token keyword keyword-int">int</span> i <span class="token operator">=</span> start<span class="token punctuation">;</span> i <span class="token operator"><=</span> tmp<span class="token punctuation">;</span> <span class="token operator">++</span>i<span class="token punctuation">)</span> <span class="token punctuation">{</span>
mp<span class="token punctuation">.</span><span class="token function">erase</span><span class="token punctuation">(</span>s<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
start <span class="token operator">=</span> tmp <span class="token operator">+</span> <span class="token number">1</span><span class="token punctuation">;</span>
mp<span class="token punctuation">[</span>s<span class="token punctuation">[</span>end<span class="token punctuation">]</span><span class="token punctuation">]</span> <span class="token operator">=</span> end<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
res <span class="token operator">=</span> std<span class="token double-colon punctuation">::</span><span class="token function">max</span><span class="token punctuation">(</span>res<span class="token punctuation">,</span> end <span class="token operator">-</span> start <span class="token operator">+</span> <span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword keyword-return">return</span> res<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</pre><ul>
<li>空间复杂度： O(n)</li>
<li>时间复杂度： O(min(m, n))</li>
<li>解法：</li>
<li>标签： <code>哈希表</code>, <code>字符串</code>, <code>滑动窗口</code></li>
<li>难度： 中等</li>
</ul>
<h1 class="mume-header" id="4-%E5%AF%BB%E6%89%BE%E4%B8%A4%E4%B8%AA%E6%AD%A3%E5%BA%8F%E6%95%B0%E7%BB%84%E7%9A%84%E4%B8%AD%E4%BD%8D%E6%95%B0">4. 寻找两个正序数组的中位数</h1>
<p>给定两个大小分别为 m 和 n 的正序（从小到大）数组 nums1 和 nums2。请你找出并返回这两个正序数组的 中位数 。</p>
<p>进阶：你能设计一个时间复杂度为 O(log (m+n)) 的算法解决此问题吗？</p>
<pre data-role="codeBlock" data-info="cpp" class="language-cpp"><span class="token comment">// https://zhuanlan.zhihu.com/p/70654378</span>
<span class="token comment">/**
*
* 如图： 假设结果i， j分别在nums1， nums2中间
* l1 i r1 l2 j r2
* |----nums1--------| |--------nums2----|
*
* i->r1 + l2->j == (nums1 + nums2) / 2 == l1->i + j->r2
* i在l1和r1之间二分搜索， 可以计算得到 l2->j = (nums1 + nums2) / 2 - l1->i
*/</span>
<span class="token keyword keyword-class">class</span> <span class="token class-name">Solution</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-public">public</span><span class="token operator">:</span>
<span class="token keyword keyword-double">double</span> <span class="token function">findMedianSortedArrays</span><span class="token punctuation">(</span>vector<span class="token operator"><</span><span class="token keyword keyword-int">int</span><span class="token operator">></span><span class="token operator">&</span> nums1<span class="token punctuation">,</span> vector<span class="token operator"><</span><span class="token keyword keyword-int">int</span><span class="token operator">></span><span class="token operator">&</span> nums2<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>nums1<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">></span> nums2<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> std<span class="token double-colon punctuation">::</span><span class="token function">swap</span><span class="token punctuation">(</span>nums1<span class="token punctuation">,</span> nums2<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>nums2<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">==</span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token keyword keyword-return">return</span> <span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">;</span> <span class="token comment">// ValueError</span>
<span class="token keyword keyword-int">int</span> iMin <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">,</span> iMax <span class="token operator">=</span> nums1<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span> halfLen <span class="token operator">=</span> <span class="token punctuation">(</span>nums1<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">+</span> nums2<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">+</span> <span class="token number">1</span><span class="token punctuation">)</span> <span class="token operator">/</span> <span class="token number">2</span><span class="token punctuation">;</span>
<span class="token keyword keyword-while">while</span> <span class="token punctuation">(</span>iMin <span class="token operator"><=</span> iMax<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-int">int</span> i <span class="token operator">=</span> iMin <span class="token operator">+</span> <span class="token punctuation">(</span>iMax <span class="token operator">-</span> iMin<span class="token punctuation">)</span> <span class="token operator">/</span> <span class="token number">2</span><span class="token punctuation">;</span>
<span class="token keyword keyword-int">int</span> j <span class="token operator">=</span> halfLen <span class="token operator">-</span> i<span class="token punctuation">;</span>
<span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>i <span class="token operator"><</span> nums1<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">&&</span> nums1<span class="token punctuation">[</span>i<span class="token punctuation">]</span> <span class="token operator"><</span> nums2<span class="token punctuation">[</span>j <span class="token operator">-</span> <span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
iMin <span class="token operator">=</span> i <span class="token operator">+</span> <span class="token number">1</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span> <span class="token keyword keyword-else">else</span> <span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>i <span class="token operator">></span> <span class="token number">0</span> <span class="token operator">&&</span> nums1<span class="token punctuation">[</span>i <span class="token operator">-</span> <span class="token number">1</span><span class="token punctuation">]</span> <span class="token operator">></span> nums2<span class="token punctuation">[</span>j<span class="token punctuation">]</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
iMax <span class="token operator">=</span> i <span class="token operator">-</span> <span class="token number">1</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span> <span class="token keyword keyword-else">else</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-int">int</span> maxLeft<span class="token punctuation">;</span>
<span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>i <span class="token operator">==</span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
maxLeft <span class="token operator">=</span> nums2<span class="token punctuation">[</span>j <span class="token operator">-</span> <span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span> <span class="token keyword keyword-else">else</span> <span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>j <span class="token operator">==</span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
maxLeft <span class="token operator">=</span> nums1<span class="token punctuation">[</span>i <span class="token operator">-</span> <span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span> <span class="token keyword keyword-else">else</span> <span class="token punctuation">{</span>
maxLeft <span class="token operator">=</span> std<span class="token double-colon punctuation">::</span><span class="token function">max</span><span class="token punctuation">(</span>nums1<span class="token punctuation">[</span>i <span class="token operator">-</span> <span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">,</span> nums2<span class="token punctuation">[</span>j <span class="token operator">-</span> <span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span><span class="token punctuation">(</span>nums1<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">+</span> nums2<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token operator">%</span> <span class="token number">2</span> <span class="token operator">==</span> <span class="token number">1</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token comment">// 中位数是一个</span>
<span class="token keyword keyword-return">return</span> maxLeft<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword keyword-int">int</span> maxRight<span class="token punctuation">;</span>
<span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>i <span class="token operator">==</span> nums1<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
maxRight <span class="token operator">=</span> nums2<span class="token punctuation">[</span>j<span class="token punctuation">]</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span> <span class="token keyword keyword-else">else</span> <span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>j <span class="token operator">==</span> nums2<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
maxRight <span class="token operator">=</span> nums1<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span> <span class="token keyword keyword-else">else</span> <span class="token punctuation">{</span>
maxRight <span class="token operator">=</span> std<span class="token double-colon punctuation">::</span><span class="token function">min</span><span class="token punctuation">(</span>nums1<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">,</span> nums2<span class="token punctuation">[</span>j<span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword keyword-return">return</span> <span class="token punctuation">(</span>maxLeft <span class="token operator">+</span> maxRight<span class="token punctuation">)</span> <span class="token operator">/</span> <span class="token number">2.0</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span class="token keyword keyword-return">return</span> <span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">;</span> <span class="token comment">// NonUse, for static check</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</pre><ul>
<li>空间复杂度： O(1)</li>
<li>时间复杂度： O(log(min(nums1.size(),nums2.size()))</li>
<li>解法： 二分查找</li>
<li>标签： <code>数组</code>, <code>二分查找</code>, <code>分治</code></li>
<li>难度： 困难</li>
</ul>
<h1 class="mume-header" id="5-%E6%9C%80%E9%95%BF%E5%9B%9E%E6%96%87%E5%AD%90%E4%B8%B2">5. 最长回文子串</h1>
<p>给你一个字符串 s，找到 s 中最长的回文子串。</p>
<pre data-role="codeBlock" data-info="cpp" class="language-cpp"><span class="token keyword keyword-class">class</span> <span class="token class-name">Solution</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-public">public</span><span class="token operator">:</span>
string <span class="token function">longestPalindrome</span><span class="token punctuation">(</span>string s<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>s<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator"><</span> <span class="token number">2</span><span class="token punctuation">)</span> <span class="token keyword keyword-return">return</span> s<span class="token punctuation">;</span>
<span class="token keyword keyword-for">for</span> <span class="token punctuation">(</span><span class="token keyword keyword-int">int</span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator"><</span> s<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token operator">++</span>i<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token function">expandAroundCenter</span><span class="token punctuation">(</span>s<span class="token punctuation">,</span> i<span class="token punctuation">,</span> i<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token function">expandAroundCenter</span><span class="token punctuation">(</span>s<span class="token punctuation">,</span> i<span class="token punctuation">,</span> i <span class="token operator">+</span> <span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword keyword-return">return</span> s<span class="token punctuation">.</span><span class="token function">substr</span><span class="token punctuation">(</span>start<span class="token punctuation">,</span> end <span class="token operator">-</span> start <span class="token operator">+</span> <span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword keyword-private">private</span><span class="token operator">:</span>
<span class="token keyword keyword-int">int</span> start <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span>
<span class="token keyword keyword-int">int</span> end <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span>
<span class="token keyword keyword-void">void</span> <span class="token function">expandAroundCenter</span><span class="token punctuation">(</span><span class="token keyword keyword-const">const</span> std<span class="token double-colon punctuation">::</span>string<span class="token operator">&</span> s<span class="token punctuation">,</span> <span class="token keyword keyword-int">int</span> l<span class="token punctuation">,</span> <span class="token keyword keyword-int">int</span> r<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-while">while</span> <span class="token punctuation">(</span>l <span class="token operator">>=</span> <span class="token number">0</span> <span class="token operator">&&</span> r <span class="token operator"><</span> s<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">&&</span> s<span class="token punctuation">[</span>l<span class="token punctuation">]</span> <span class="token operator">==</span> s<span class="token punctuation">[</span>r<span class="token punctuation">]</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
l<span class="token operator">--</span><span class="token punctuation">;</span>
r<span class="token operator">++</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>r <span class="token operator">-</span> l <span class="token operator">-</span> <span class="token number">2</span> <span class="token operator">></span> end <span class="token operator">-</span> start<span class="token punctuation">)</span> <span class="token punctuation">{</span>
start <span class="token operator">=</span> l <span class="token operator">+</span> <span class="token number">1</span><span class="token punctuation">;</span>
end <span class="token operator">=</span> r <span class="token operator">-</span> <span class="token number">1</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</pre><ul>
<li>空间复杂度： O(1)</li>
<li>时间复杂度： O(n^2)</li>
<li>解法： 中心扩展算法</li>
<li>标签： <code>字符串</code>, <code>动态规划</code></li>
<li>难度： 中等</li>
</ul>
<h1 class="mume-header" id="7-%E6%95%B4%E6%95%B0%E5%8F%8D%E8%BD%AC">7. 整数反转</h1>
<p>给你一个 32 位的有符号整数 x ，返回将 x 中的数字部分反转后的结果。</p>
<p>如果反转后整数超过 32 位的有符号整数的范围 [−231, 231 − 1] ，就返回 0。</p>
<p>假设环境不允许存储 64 位整数（有符号或无符号）。</p>
<pre data-role="codeBlock" data-info="cpp" class="language-cpp"><span class="token keyword keyword-class">class</span> <span class="token class-name">Solution</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-public">public</span><span class="token operator">:</span>
<span class="token keyword keyword-int">int</span> <span class="token function">reverse</span><span class="token punctuation">(</span><span class="token keyword keyword-int">int</span> x<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-long">long</span> <span class="token keyword keyword-long">long</span> <span class="token keyword keyword-int">int</span> res <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span>
<span class="token keyword keyword-while">while</span> <span class="token punctuation">(</span>x <span class="token operator">!=</span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
res <span class="token operator">=</span> res <span class="token operator">*</span> <span class="token number">10</span> <span class="token operator">+</span> x <span class="token operator">%</span> <span class="token number">10</span><span class="token punctuation">;</span>
x <span class="token operator">=</span> x <span class="token operator">/</span> <span class="token number">10</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword keyword-return">return</span> <span class="token punctuation">(</span>res <span class="token operator"><</span> INT_MIN <span class="token operator">||</span> res <span class="token operator">></span> INT_MAX<span class="token punctuation">)</span> <span class="token operator">?</span> <span class="token number">0</span> <span class="token operator">:</span> res<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</pre><ul>
<li>空间复杂度： O(1)</li>
<li>时间复杂度： O(n)</li>
<li>解法：</li>
<li>标签： <code>数学</code></li>
<li>难度： 简单</li>
</ul>
<h1 class="mume-header" id="8-%E5%AD%97%E7%AC%A6%E4%B8%B2%E8%BD%AC%E6%8D%A2%E6%95%B4%E6%95%B0-atoi">8. 字符串转换整数 (atoi)</h1>
<p>请你来实现一个 myAtoi(string s) 函数，使其能将字符串转换成一个 32 位有符号整数（类似 C/C++ 中的 atoi 函数）。</p>
<p>函数 myAtoi(string s) 的算法如下：</p>
<p>读入字符串并丢弃无用的前导空格<br>
检查下一个字符（假设还未到字符末尾）为正还是负号，读取该字符（如果有）。 确定最终结果是负数还是正数。 如果两者都不存在，则假定结果为正。<br>
读入下一个字符，直到到达下一个非数字字符或到达输入的结尾。字符串的其余部分将被忽略。<br>
将前面步骤读入的这些数字转换为整数（即，"123" -> 123， "0032" -> 32）。如果没有读入数字，则整数为 0 。必要时更改符号（从步骤 2 开始）。<br>
如果整数数超过 32 位有符号整数范围 [−2^31, 2^31 − 1] ，需要截断这个整数，使其保持在这个范围内。具体来说，小于 −2^31 的整数应该被固定为 −2^31 ，大于 2^31 − 1 的整数应该被固定为 2^31 − 1 。<br>
返回整数作为最终结果。</p>
<p>注意：</p>
<p>本题中的空白字符只包括空格字符 ' ' 。<br>
除前导空格或数字后的其余字符串外，请勿忽略 任何其他字符。</p>
<pre data-role="codeBlock" data-info="cpp" class="language-cpp"><span class="token keyword keyword-class">class</span> <span class="token class-name">Solution</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-public">public</span><span class="token operator">:</span>
<span class="token keyword keyword-int">int</span> <span class="token function">myAtoi</span><span class="token punctuation">(</span>string s<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-long">long</span> <span class="token keyword keyword-int">int</span> result <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span>
<span class="token keyword keyword-int">int</span> indicator <span class="token operator">=</span> <span class="token number">1</span><span class="token punctuation">;</span>
<span class="token keyword keyword-int">int</span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span>
i <span class="token operator">=</span> s<span class="token punctuation">.</span><span class="token function">find_first_not_of</span><span class="token punctuation">(</span><span class="token string">' '</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>i <span class="token operator"><</span> s<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">&&</span> <span class="token punctuation">(</span>s<span class="token punctuation">[</span>i<span class="token punctuation">]</span> <span class="token operator">==</span> <span class="token string">'-'</span> <span class="token operator">||</span> s<span class="token punctuation">[</span>i<span class="token punctuation">]</span> <span class="token operator">==</span> <span class="token string">'+'</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
indicator <span class="token operator">=</span> <span class="token punctuation">(</span>s<span class="token punctuation">[</span>i<span class="token punctuation">]</span> <span class="token operator">==</span> <span class="token string">'-'</span><span class="token punctuation">)</span> <span class="token operator">?</span> <span class="token operator">-</span><span class="token number">1</span> <span class="token operator">:</span> <span class="token number">1</span><span class="token punctuation">;</span>
i<span class="token operator">++</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword keyword-while">while</span> <span class="token punctuation">(</span>i <span class="token operator"><</span> s<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">&&</span> <span class="token punctuation">(</span><span class="token string">'0'</span> <span class="token operator"><=</span> s<span class="token punctuation">[</span>i<span class="token punctuation">]</span> <span class="token operator">&&</span> s<span class="token punctuation">[</span>i<span class="token punctuation">]</span> <span class="token operator"><=</span> <span class="token string">'9'</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
result <span class="token operator">=</span> result <span class="token operator">*</span> <span class="token number">10</span> <span class="token operator">+</span> <span class="token punctuation">(</span>s<span class="token punctuation">[</span>i<span class="token punctuation">]</span> <span class="token operator">-</span> <span class="token string">'0'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
i<span class="token operator">++</span><span class="token punctuation">;</span>
<span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>result <span class="token operator">*</span> indicator <span class="token operator">>=</span> std<span class="token double-colon punctuation">::</span><span class="token class-name">numeric_limits</span><span class="token operator"><</span><span class="token keyword keyword-int">int</span><span class="token operator">></span><span class="token double-colon punctuation">::</span><span class="token function">max</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token keyword keyword-return">return</span> std<span class="token double-colon punctuation">::</span><span class="token class-name">numeric_limits</span><span class="token operator"><</span><span class="token keyword keyword-int">int</span><span class="token operator">></span><span class="token double-colon punctuation">::</span><span class="token function">max</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>result <span class="token operator">*</span> indicator <span class="token operator"><=</span> std<span class="token double-colon punctuation">::</span><span class="token class-name">numeric_limits</span><span class="token operator"><</span><span class="token keyword keyword-int">int</span><span class="token operator">></span><span class="token double-colon punctuation">::</span><span class="token function">min</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token keyword keyword-return">return</span> std<span class="token double-colon punctuation">::</span><span class="token class-name">numeric_limits</span><span class="token operator"><</span><span class="token keyword keyword-int">int</span><span class="token operator">></span><span class="token double-colon punctuation">::</span><span class="token function">min</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword keyword-return">return</span> result <span class="token operator">*</span> indicator<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</pre><ul>
<li>空间复杂度： O(1)</li>
<li>时间复杂度： O(n)</li>
<li>解法：</li>
<li>标签： <code>字符串</code></li>
<li>难度： 中等</li>
</ul>
<h1 class="mume-header" id="10-%E6%AD%A3%E5%88%99%E8%A1%A8%E8%BE%BE%E5%BC%8F%E5%8C%B9%E9%85%8D">10. 正则表达式匹配</h1>
<p>TODO:</p>
<h1 class="mume-header" id="11-%E7%9B%9B%E6%9C%80%E5%A4%9A%E6%B0%B4%E7%9A%84%E5%AE%B9%E5%99%A8">11. 盛最多水的容器</h1>
<p>给你 n 个非负整数 a1，a2，...，an，每个数代表坐标中的一个点 (i, ai) 。在坐标内画 n 条垂直线，垂直线 i 的两个端点分别为 (i, ai) 和 (i, 0) 。找出其中的两条线，使得它们与 x 轴共同构成的容器可以容纳最多的水。</p>
<p>说明：你不能倾斜容器。</p>
<p>输入：[1,8,6,2,5,4,8,3,7]<br>
输出：49<br>
解释：图中垂直线代表输入数组 [1,8,6,2,5,4,8,3,7]。在此情况下，容器能够容纳水（表示为蓝色部分）的最大值为 49。</p>
<pre data-role="codeBlock" data-info="cpp" class="language-cpp"><span class="token keyword keyword-class">class</span> <span class="token class-name">Solution</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-public">public</span><span class="token operator">:</span>
<span class="token keyword keyword-int">int</span> <span class="token function">maxArea</span><span class="token punctuation">(</span>vector<span class="token operator"><</span><span class="token keyword keyword-int">int</span><span class="token operator">></span><span class="token operator">&</span> height<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-int">int</span> maxSpace <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">,</span> l <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">,</span> r <span class="token operator">=</span> height<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">-</span> <span class="token number">1</span><span class="token punctuation">;</span>
<span class="token keyword keyword-while">while</span> <span class="token punctuation">(</span>l <span class="token operator"><</span> r<span class="token punctuation">)</span> <span class="token punctuation">{</span>
maxSpace <span class="token operator">=</span> std<span class="token double-colon punctuation">::</span><span class="token function">max</span><span class="token punctuation">(</span>maxSpace<span class="token punctuation">,</span> std<span class="token double-colon punctuation">::</span><span class="token function">min</span><span class="token punctuation">(</span>height<span class="token punctuation">[</span>l<span class="token punctuation">]</span><span class="token punctuation">,</span> height<span class="token punctuation">[</span>r<span class="token punctuation">]</span><span class="token punctuation">)</span> <span class="token operator">*</span> <span class="token punctuation">(</span>r <span class="token operator">-</span> l<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
height<span class="token punctuation">[</span>l<span class="token punctuation">]</span> <span class="token operator">></span> height<span class="token punctuation">[</span>r<span class="token punctuation">]</span> <span class="token operator">?</span> r<span class="token operator">--</span> <span class="token operator">:</span> l<span class="token operator">++</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword keyword-return">return</span> maxSpace<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</pre><ul>
<li>空间复杂度： O(1)</li>
<li>时间复杂度： O(n)</li>
<li>解法： 双指针+贪心</li>
<li>标签： <code>贪心</code>, <code>数组</code>, <code>双指针</code></li>
<li>难度： 中等</li>
</ul>
<h1 class="mume-header" id="13-%E7%BD%97%E9%A9%AC%E6%95%B0%E5%AD%97%E8%BD%AC%E6%95%B4%E6%95%B0">13. 罗马数字转整数</h1>
<p>罗马数字包含以下七种字符: I， V， X， L，C，D 和 M。</p>
<pre data-role="codeBlock" data-info="txt" class="language-txt">字符 数值
I 1
V 5
X 10
L 50
C 100
D 500
M 1000
</pre><p>例如， 罗马数字 2 写做 II ，即为两个并列的 1。12 写做 XII ，即为 X + II 。 27 写做 XXVII, 即为 XX + V + II 。</p>
<p>通常情况下，罗马数字中小的数字在大的数字的右边。但也存在特例，例如 4 不写做 IIII，而是 IV。数字 1 在数字 5 的左边，所表示的数等于大数 5 减小数 1 得到的数值 4 。同样地，数字 9 表示为 IX。这个特殊的规则只适用于以下六种情况：</p>
<p>I 可以放在 V (5) 和 X (10) 的左边，来表示 4 和 9。<br>
X 可以放在 L (50) 和 C (100) 的左边，来表示 40 和 90。 <br>
C 可以放在 D (500) 和 M (1000) 的左边，来表示 400 和 900。<br>
给定一个罗马数字，将其转换成整数。输入确保在 1 到 3999 的范围内。</p>
<pre data-role="codeBlock" data-info="cpp" class="language-cpp"><span class="token keyword keyword-class">class</span> <span class="token class-name">Solution</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-public">public</span><span class="token operator">:</span>
<span class="token keyword keyword-int">int</span> <span class="token function">romanToInt</span><span class="token punctuation">(</span>string s<span class="token punctuation">)</span> <span class="token punctuation">{</span>
std<span class="token double-colon punctuation">::</span>map<span class="token operator"><</span><span class="token keyword keyword-char">char</span><span class="token punctuation">,</span> <span class="token keyword keyword-int">int</span><span class="token operator">></span> mp <span class="token operator">=</span> <span class="token punctuation">{</span>
<span class="token punctuation">{</span><span class="token string">'I'</span><span class="token punctuation">,</span> <span class="token number">1</span><span class="token punctuation">}</span><span class="token punctuation">,</span>
<span class="token punctuation">{</span><span class="token string">'V'</span><span class="token punctuation">,</span> <span class="token number">5</span><span class="token punctuation">}</span><span class="token punctuation">,</span>
<span class="token punctuation">{</span><span class="token string">'X'</span><span class="token punctuation">,</span> <span class="token number">10</span><span class="token punctuation">}</span><span class="token punctuation">,</span>
<span class="token punctuation">{</span><span class="token string">'L'</span><span class="token punctuation">,</span> <span class="token number">50</span><span class="token punctuation">}</span><span class="token punctuation">,</span>
<span class="token punctuation">{</span><span class="token string">'C'</span><span class="token punctuation">,</span> <span class="token number">100</span><span class="token punctuation">}</span><span class="token punctuation">,</span>
<span class="token punctuation">{</span><span class="token string">'D'</span><span class="token punctuation">,</span> <span class="token number">500</span><span class="token punctuation">}</span><span class="token punctuation">,</span>
<span class="token punctuation">{</span><span class="token string">'M'</span><span class="token punctuation">,</span> <span class="token number">1000</span><span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
<span class="token keyword keyword-int">int</span> res <span class="token operator">=</span> mp<span class="token punctuation">[</span>s<span class="token punctuation">[</span>s<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">-</span> <span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
<span class="token keyword keyword-for">for</span> <span class="token punctuation">(</span><span class="token keyword keyword-int">int</span> i <span class="token operator">=</span> s<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">-</span> <span class="token number">2</span><span class="token punctuation">;</span> i <span class="token operator">>=</span> <span class="token number">0</span><span class="token punctuation">;</span> <span class="token operator">--</span>i<span class="token punctuation">)</span> <span class="token punctuation">{</span>
res <span class="token operator">+=</span> mp<span class="token punctuation">[</span>s<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">]</span> <span class="token operator"><</span> mp<span class="token punctuation">[</span>s<span class="token punctuation">[</span>i <span class="token operator">+</span> <span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">]</span> <span class="token operator">?</span> <span class="token operator">-</span>mp<span class="token punctuation">[</span>s<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">]</span> <span class="token operator">:</span> mp<span class="token punctuation">[</span>s<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword keyword-return">return</span> res<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</pre><ul>
<li>空间复杂度： O(1)</li>
<li>时间复杂度： O(n)</li>
<li>解法：</li>
<li>标签： <code>哈希表</code>, <code>数学</code>, <code>字符串</code></li>
<li>难度： 简单</li>
</ul>
<h1 class="mume-header" id="14-%E6%9C%80%E9%95%BF%E5%85%AC%E5%85%B1%E5%89%8D%E7%BC%80">14. 最长公共前缀</h1>
<p>编写一个函数来查找字符串数组中的最长公共前缀。</p>
<p>如果不存在公共前缀，返回空字符串 ""。</p>
<pre data-role="codeBlock" data-info="cpp" class="language-cpp"><span class="token keyword keyword-class">class</span> <span class="token class-name">Solution</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-public">public</span><span class="token operator">:</span>
string <span class="token function">longestCommonPrefix</span><span class="token punctuation">(</span>vector<span class="token operator"><</span>string<span class="token operator">></span><span class="token operator">&</span> strs<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>strs<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">==</span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token keyword keyword-return">return</span> <span class="token string">""</span><span class="token punctuation">;</span>
<span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>strs<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">==</span> <span class="token number">1</span><span class="token punctuation">)</span> <span class="token keyword keyword-return">return</span> strs<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
<span class="token keyword keyword-int">int</span> iterLen <span class="token operator">=</span> std<span class="token double-colon punctuation">::</span><span class="token class-name">numeric_limits</span><span class="token operator"><</span><span class="token keyword keyword-int">int</span><span class="token operator">></span><span class="token double-colon punctuation">::</span><span class="token function">max</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword keyword-for">for</span> <span class="token punctuation">(</span><span class="token keyword keyword-const">const</span> std<span class="token double-colon punctuation">::</span>string s <span class="token operator">:</span> strs<span class="token punctuation">)</span> iterLen <span class="token operator">=</span> std<span class="token double-colon punctuation">::</span><span class="token function">min</span><span class="token punctuation">(</span>iterLen<span class="token punctuation">,</span> <span class="token punctuation">(</span><span class="token keyword keyword-int">int</span><span class="token punctuation">)</span>s<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
std<span class="token double-colon punctuation">::</span>string res<span class="token punctuation">;</span>
<span class="token keyword keyword-for">for</span> <span class="token punctuation">(</span><span class="token keyword keyword-int">int</span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator"><</span> iterLen<span class="token punctuation">;</span> <span class="token operator">++</span>i<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-int">int</span> j <span class="token operator">=</span> <span class="token number">1</span><span class="token punctuation">;</span>
<span class="token keyword keyword-while">while</span> <span class="token punctuation">(</span>j <span class="token operator"><</span> strs<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">&&</span> strs<span class="token punctuation">[</span>j <span class="token operator">-</span> <span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">[</span>i<span class="token punctuation">]</span> <span class="token operator">==</span> strs<span class="token punctuation">[</span>j<span class="token punctuation">]</span><span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">)</span> j<span class="token operator">++</span><span class="token punctuation">;</span>
<span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>j <span class="token operator">==</span> strs<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
res <span class="token operator">+=</span> strs<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span> <span class="token keyword keyword-else">else</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-break">break</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span class="token keyword keyword-return">return</span> res<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</pre><ul>
<li>空间复杂度： O(1)</li>
<li>时间复杂度： O(n^2)</li>
<li>解法： 双循环，字典树</li>
<li>标签： <code>字符串</code></li>
<li>难度： 简单</li>
</ul>
<p>FIXME: 字典树解法 <a href="https://leetcode.com/problems/longest-common-prefix/solution/">https://leetcode.com/problems/longest-common-prefix/solution/</a></p>
<h1 class="mume-header" id="15-%E4%B8%89%E6%95%B0%E4%B9%8B%E5%92%8C">15. 三数之和</h1>
<p>给你一个包含 n 个整数的数组 nums，判断 nums 中是否存在三个元素 a，b，c ，使得 a + b + c = 0 ？请你找出所有和为 0 且不重复的三元组。</p>
<p>注意：答案中不可以包含重复的三元组。</p>
<p>示例 1：</p>
<p>输入：nums = [-1,0,1,2,-1,-4]<br>
输出：<a href="file:///Users/bytedance/Documents/git-repos/Leetcode/-1,-1,2],[-1,0,1.md">-1,-1,2],[-1,0,1</a><br>
示例 2：</p>
<p>输入：nums = []<br>
输出：[]<br>
示例 3：</p>
<p>输入：nums = [0]<br>
输出：[]</p>
<p>提示：</p>
<p>0 <= nums.length <= 3000<br>
-10^5 <= nums[i] <= 10^5</p>
<pre data-role="codeBlock" data-info="cpp" class="language-cpp"><span class="token keyword keyword-class">class</span> <span class="token class-name">Solution</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-public">public</span><span class="token operator">:</span>
vector<span class="token operator"><</span>vector<span class="token operator"><</span><span class="token keyword keyword-int">int</span><span class="token operator">>></span> <span class="token function">threeSum</span><span class="token punctuation">(</span>vector<span class="token operator"><</span><span class="token keyword keyword-int">int</span><span class="token operator">></span><span class="token operator">&</span> nums<span class="token punctuation">)</span> <span class="token punctuation">{</span>
std<span class="token double-colon punctuation">::</span>vector<span class="token operator"><</span>std<span class="token double-colon punctuation">::</span>vector<span class="token operator"><</span><span class="token keyword keyword-int">int</span><span class="token operator">>></span> res<span class="token punctuation">;</span>
std<span class="token double-colon punctuation">::</span><span class="token function">sort</span><span class="token punctuation">(</span>nums<span class="token punctuation">.</span><span class="token function">begin</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span> nums<span class="token punctuation">.</span><span class="token function">end</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword keyword-for">for</span> <span class="token punctuation">(</span><span class="token keyword keyword-int">int</span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator"><</span> <span class="token punctuation">(</span><span class="token keyword keyword-int">int</span><span class="token punctuation">)</span> nums<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">-</span> <span class="token number">2</span><span class="token punctuation">;</span> <span class="token operator">++</span>i<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>i <span class="token operator">></span> <span class="token number">0</span> <span class="token operator">&&</span> nums<span class="token punctuation">[</span>i<span class="token punctuation">]</span> <span class="token operator">==</span> nums<span class="token punctuation">[</span>i <span class="token operator">-</span> <span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">)</span> <span class="token keyword keyword-continue">continue</span><span class="token punctuation">;</span> <span class="token comment">// result remove repeat</span>
<span class="token keyword keyword-int">int</span> j <span class="token operator">=</span> i <span class="token operator">+</span> <span class="token number">1</span><span class="token punctuation">,</span> k <span class="token operator">=</span> nums<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">-</span> <span class="token number">1</span><span class="token punctuation">;</span>
<span class="token keyword keyword-while">while</span> <span class="token punctuation">(</span>j <span class="token operator"><</span> k<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-int">int</span> sm <span class="token operator">=</span> nums<span class="token punctuation">[</span>i<span class="token punctuation">]</span> <span class="token operator">+</span> nums<span class="token punctuation">[</span>j<span class="token punctuation">]</span> <span class="token operator">+</span> nums<span class="token punctuation">[</span>k<span class="token punctuation">]</span><span class="token punctuation">;</span>
<span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>sm <span class="token operator">==</span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
res<span class="token punctuation">.</span><span class="token function">push_back</span><span class="token punctuation">(</span>std<span class="token double-colon punctuation">::</span>vector<span class="token operator"><</span><span class="token keyword keyword-int">int</span><span class="token operator">></span><span class="token punctuation">{</span> nums<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">,</span> nums<span class="token punctuation">[</span>j<span class="token punctuation">]</span><span class="token punctuation">,</span> nums<span class="token punctuation">[</span>k<span class="token punctuation">]</span> <span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword keyword-while">while</span> <span class="token punctuation">(</span>j <span class="token operator">+</span> <span class="token number">1</span> <span class="token operator"><</span> k <span class="token operator">&&</span> nums<span class="token punctuation">[</span>j<span class="token punctuation">]</span> <span class="token operator">==</span> nums<span class="token punctuation">[</span>j <span class="token operator">+</span> <span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">)</span> j<span class="token operator">++</span><span class="token punctuation">;</span>
<span class="token keyword keyword-while">while</span> <span class="token punctuation">(</span>j <span class="token operator"><</span> k <span class="token operator">-</span> <span class="token number">1</span> <span class="token operator">&&</span> nums<span class="token punctuation">[</span>k<span class="token punctuation">]</span> <span class="token operator">==</span> nums<span class="token punctuation">[</span>k <span class="token operator">-</span> <span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">)</span> k<span class="token operator">--</span><span class="token punctuation">;</span>
j<span class="token operator">++</span><span class="token punctuation">;</span>
k<span class="token operator">--</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span> <span class="token keyword keyword-else">else</span> <span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>sm <span class="token operator">></span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
k<span class="token operator">--</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span> <span class="token keyword keyword-else">else</span> <span class="token punctuation">{</span> <span class="token comment">// sm < 0</span>
j<span class="token operator">++</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span class="token keyword keyword-return">return</span> res<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</pre><ul>
<li>空间复杂度：</li>
<li>时间复杂度： O(n ^ 2)</li>
<li>解法： 双指针</li>
<li>标签： <code>数组</code>, <code>双指针</code>, <code>排序</code></li>
<li>难度： 中等</li>
</ul>
<h1 class="mume-header" id="17-%E7%94%B5%E8%AF%9D%E5%8F%B7%E7%A0%81%E7%9A%84%E5%AD%97%E6%AF%8D%E7%BB%84%E5%90%88">17. 电话号码的字母组合</h1>
<p>给定一个仅包含数字 2-9 的字符串，返回所有它能表示的字母组合。答案可以按 任意顺序 返回。</p>
<p>给出数字到字母的映射如下（与电话按键相同）。注意 1 不对应任何字母。</p>
<p>示例 1：</p>
<p>输入：digits = "23"<br>
输出：["ad","ae","af","bd","be","bf","cd","ce","cf"]<br>
示例 2：</p>
<p>输入：digits = ""<br>
输出：[]<br>
示例 3：</p>
<p>输入：digits = "2"<br>
输出：["a","b","c"]</p>
<pre data-role="codeBlock" data-info="cpp" class="language-cpp"><span class="token keyword keyword-class">class</span> <span class="token class-name">Solution</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-public">public</span><span class="token operator">:</span>
vector<span class="token operator"><</span>string<span class="token operator">></span> <span class="token function">letterCombinations</span><span class="token punctuation">(</span>string digits<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>digits<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">==</span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token keyword keyword-return">return</span> <span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">;</span>
std<span class="token double-colon punctuation">::</span>vector<span class="token operator"><</span>std<span class="token double-colon punctuation">::</span>string<span class="token operator">></span> mp <span class="token operator">=</span> <span class="token punctuation">{</span><span class="token string">"0"</span><span class="token punctuation">,</span> <span class="token string">"1"</span><span class="token punctuation">,</span> <span class="token string">"abc"</span><span class="token punctuation">,</span> <span class="token string">"def"</span><span class="token punctuation">,</span> <span class="token string">"ghi"</span><span class="token punctuation">,</span> <span class="token string">"jkl"</span><span class="token punctuation">,</span> <span class="token string">"mno"</span><span class="token punctuation">,</span> <span class="token string">"pqrs"</span><span class="token punctuation">,</span> <span class="token string">"tuv"</span><span class="token punctuation">,</span> <span class="token string">"wxyz"</span><span class="token punctuation">}</span><span class="token punctuation">;</span>
std<span class="token double-colon punctuation">::</span>vector<span class="token operator"><</span>std<span class="token double-colon punctuation">::</span>string<span class="token operator">></span> result<span class="token punctuation">;</span>
result<span class="token punctuation">.</span><span class="token function">push_back</span><span class="token punctuation">(</span><span class="token string">""</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword keyword-for">for</span> <span class="token punctuation">(</span><span class="token keyword keyword-const">const</span> <span class="token keyword keyword-char">char</span><span class="token operator">&</span> ch <span class="token operator">:</span> digits<span class="token punctuation">)</span> <span class="token punctuation">{</span>
std<span class="token double-colon punctuation">::</span>vector<span class="token operator"><</span>std<span class="token double-colon punctuation">::</span>string<span class="token operator">></span> tmp<span class="token punctuation">;</span>
<span class="token keyword keyword-for">for</span> <span class="token punctuation">(</span><span class="token keyword keyword-const">const</span> <span class="token keyword keyword-char">char</span><span class="token operator">&</span> t <span class="token operator">:</span> mp<span class="token punctuation">[</span>ch <span class="token operator">-</span> <span class="token string">'0'</span><span class="token punctuation">]</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-for">for</span> <span class="token punctuation">(</span>std<span class="token double-colon punctuation">::</span>string<span class="token operator">&</span> s <span class="token operator">:</span> result<span class="token punctuation">)</span> <span class="token punctuation">{</span>
tmp<span class="token punctuation">.</span><span class="token function">push_back</span><span class="token punctuation">(</span>s <span class="token operator">+</span> t<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
result<span class="token punctuation">.</span><span class="token function">swap</span><span class="token punctuation">(</span>tmp<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword keyword-return">return</span> result<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</pre><ul>
<li>空间复杂度： O(result.size())</li>
<li>时间复杂度： O(digits.size())</li>
<li>解法：</li>
<li>标签： <code>哈希表</code>, <code>字符串</code>, <code>回溯</code></li>
<li>难度： 中等</li>
</ul>
<h1 class="mume-header" id="19-%E5%88%A0%E9%99%A4%E9%93%BE%E8%A1%A8%E7%9A%84%E5%80%92%E6%95%B0%E7%AC%AC-n-%E4%B8%AA%E7%BB%93%E7%82%B9">19. 删除链表的倒数第 N 个结点</h1>
<p>给你一个链表，删除链表的倒数第 n 个结点，并且返回链表的头结点。</p>
<p>进阶：你能尝试使用一趟扫描实现吗？</p>
<p>示例 1：<br>
输入：head = [1,2,3,4,5], n = 2<br>
输出：[1,2,3,5]</p>
<pre data-role="codeBlock" data-info="cpp" class="language-cpp"><span class="token comment">/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode() : val(0), next(nullptr) {}
* ListNode(int x) : val(x), next(nullptr) {}
* ListNode(int x, ListNode *next) : val(x), next(next) {}
* };
*/</span>
<span class="token keyword keyword-class">class</span> <span class="token class-name">Solution</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-public">public</span><span class="token operator">:</span>
ListNode<span class="token operator">*</span> <span class="token function">removeNthFromEnd</span><span class="token punctuation">(</span>ListNode<span class="token operator">*</span> head<span class="token punctuation">,</span> <span class="token keyword keyword-int">int</span> n<span class="token punctuation">)</span> <span class="token punctuation">{</span>
ListNode<span class="token operator">*</span> dummy <span class="token operator">=</span> <span class="token keyword keyword-new">new</span> <span class="token function">ListNode</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
dummy<span class="token operator">-></span>next <span class="token operator">=</span> head<span class="token punctuation">;</span>
ListNode<span class="token operator">*</span> slow <span class="token operator">=</span> dummy<span class="token punctuation">;</span>
ListNode<span class="token operator">*</span> fast <span class="token operator">=</span> dummy<span class="token punctuation">;</span>
<span class="token keyword keyword-while">while</span> <span class="token punctuation">(</span>n <span class="token operator">>=</span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
fast <span class="token operator">=</span> fast<span class="token operator">-></span>next<span class="token punctuation">;</span>
n<span class="token operator">--</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword keyword-while">while</span> <span class="token punctuation">(</span>fast <span class="token operator">!=</span> <span class="token keyword keyword-nullptr">nullptr</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
fast <span class="token operator">=</span> fast<span class="token operator">-></span>next<span class="token punctuation">;</span>
slow <span class="token operator">=</span> slow<span class="token operator">-></span>next<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
slow<span class="token operator">-></span>next <span class="token operator">=</span> slow<span class="token operator">-></span>next<span class="token operator">-></span>next<span class="token punctuation">;</span>
<span class="token keyword keyword-return">return</span> dummy<span class="token operator">-></span>next<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</pre><ul>
<li>空间复杂度： O(1)</li>
<li>时间复杂度： O(n)</li>
<li>解法： 快慢指针</li>
<li>标签： <code>链表</code>, <code>双指针</code></li>
<li>难度： 中等</li>
</ul>
<h1 class="mume-header" id="20-%E6%9C%89%E6%95%88%E7%9A%84%E6%8B%AC%E5%8F%B7">20. 有效的括号</h1>
<p>给定一个只包括 '('，')'，'{'，'}'，'['，']' 的字符串 s ，判断字符串是否有效。</p>
<p>有效字符串需满足：</p>
<p>左括号必须用相同类型的右括号闭合。<br>
左括号必须以正确的顺序闭合。</p>
<p>提示：</p>
<p>1 <= s.length <= 10^4<br>
s 仅由括号 '()[]{}' 组成</p>
<pre data-role="codeBlock" data-info="cpp" class="language-cpp"><span class="token keyword keyword-class">class</span> <span class="token class-name">Solution</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-public">public</span><span class="token operator">:</span>
<span class="token keyword keyword-bool">bool</span> <span class="token function">isValid</span><span class="token punctuation">(</span>string s<span class="token punctuation">)</span> <span class="token punctuation">{</span>
std<span class="token double-colon punctuation">::</span>stack<span class="token operator"><</span><span class="token keyword keyword-char">char</span><span class="token operator">></span> stk<span class="token punctuation">;</span>
<span class="token keyword keyword-for">for</span> <span class="token punctuation">(</span><span class="token keyword keyword-const">const</span> <span class="token keyword keyword-char">char</span><span class="token operator">&</span> ch <span class="token operator">:</span> s<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>ch <span class="token operator">==</span> <span class="token string">'('</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
stk<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span><span class="token string">')'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span> <span class="token keyword keyword-else">else</span> <span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>ch <span class="token operator">==</span> <span class="token string">'{'</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
stk<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span><span class="token string">'}'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span> <span class="token keyword keyword-else">else</span> <span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>ch <span class="token operator">==</span> <span class="token string">'['</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
stk<span class="token punctuation">.</span><span class="token function">push</span><span class="token punctuation">(</span><span class="token string">']'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span> <span class="token keyword keyword-else">else</span> <span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>stk<span class="token punctuation">.</span><span class="token function">empty</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">||</span> stk<span class="token punctuation">.</span><span class="token function">top</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">!=</span> ch<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-return">return</span> <span class="token boolean">false</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span> <span class="token keyword keyword-else">else</span> <span class="token punctuation">{</span>
stk<span class="token punctuation">.</span><span class="token function">pop</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span class="token keyword keyword-return">return</span> stk<span class="token punctuation">.</span><span class="token function">empty</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</pre><ul>
<li>空间复杂度： O(n)</li>
<li>时间复杂度： O(n)</li>
<li>解法：</li>
<li>标签： <code>栈</code>, <code>字符串</code></li>
<li>难度： 简单</li>
</ul>
<h1 class="mume-header" id="21-%E5%90%88%E5%B9%B6%E4%B8%A4%E4%B8%AA%E6%9C%89%E5%BA%8F%E9%93%BE%E8%A1%A8">21. 合并两个有序链表</h1>
<p>将两个升序链表合并为一个新的 升序 链表并返回。新链表是通过拼接给定的两个链表的所有节点组成的。</p>
<p>输入：l1 = [1,2,4], l2 = [1,3,4]<br>
输出：[1,1,2,3,4,4]<br>
示例 2：</p>
<p>输入：l1 = [], l2 = []<br>
输出：[]<br>
示例 3：</p>
<p>输入：l1 = [], l2 = [0]<br>
输出：[0]</p>
<p>提示：</p>
<p>两个链表的节点数目范围是 [0, 50]<br>
-100 <= Node.val <= 100<br>
l1 和 l2 均按 非递减顺序 排列</p>
<pre data-role="codeBlock" data-info="cpp" class="language-cpp"><span class="token comment">/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode() : val(0), next(nullptr) {}
* ListNode(int x) : val(x), next(nullptr) {}
* ListNode(int x, ListNode *next) : val(x), next(next) {}
* };
*/</span>
<span class="token keyword keyword-class">class</span> <span class="token class-name">Solution</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-public">public</span><span class="token operator">:</span>
ListNode<span class="token operator">*</span> <span class="token function">mergeTwoLists</span><span class="token punctuation">(</span>ListNode<span class="token operator">*</span> l1<span class="token punctuation">,</span> ListNode<span class="token operator">*</span> l2<span class="token punctuation">)</span> <span class="token punctuation">{</span>
ListNode<span class="token operator">*</span> root <span class="token operator">=</span> <span class="token keyword keyword-new">new</span> <span class="token function">ListNode</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
ListNode<span class="token operator">*</span> cur <span class="token operator">=</span> root<span class="token punctuation">;</span>
<span class="token keyword keyword-while">while</span> <span class="token punctuation">(</span>l1 <span class="token operator">!=</span> <span class="token keyword keyword-nullptr">nullptr</span> <span class="token operator">&&</span> l2 <span class="token operator">!=</span> <span class="token keyword keyword-nullptr">nullptr</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>l1<span class="token operator">-></span>val <span class="token operator"><</span> l2<span class="token operator">-></span>val<span class="token punctuation">)</span> <span class="token punctuation">{</span>
cur<span class="token operator">-></span>next <span class="token operator">=</span> l1<span class="token punctuation">;</span>
l1 <span class="token operator">=</span> l1<span class="token operator">-></span>next<span class="token punctuation">;</span>
<span class="token punctuation">}</span> <span class="token keyword keyword-else">else</span> <span class="token punctuation">{</span> <span class="token comment">// l1->val >= l2->val</span>
cur<span class="token operator">-></span>next <span class="token operator">=</span> l2<span class="token punctuation">;</span>
l2 <span class="token operator">=</span> l2<span class="token operator">-></span>next<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
cur <span class="token operator">=</span> cur<span class="token operator">-></span>next<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
cur<span class="token operator">-></span>next <span class="token operator">=</span> l1 <span class="token operator">!=</span> <span class="token keyword keyword-nullptr">nullptr</span> <span class="token operator">?</span> l1 <span class="token operator">:</span> l2<span class="token punctuation">;</span>
<span class="token keyword keyword-return">return</span> root<span class="token operator">-></span>next<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</pre><ul>
<li>空间复杂度： O(1)</li>
<li>时间复杂度： O(n)</li>
<li>解法：</li>
<li>标签： <code>递归</code>, <code>链表</code></li>
<li>难度： 简单</li>
</ul>
<h1 class="mume-header" id="22-%E6%8B%AC%E5%8F%B7%E7%94%9F%E6%88%90">22. 括号生成</h1>
<p>数字 n 代表生成括号的对数，请你设计一个函数，用于能够生成所有可能的并且 有效的 括号组合。</p>
<p>示例 1：</p>
<p>输入：n = 3<br>
输出：["((()))","(()())","(())()","()(())","()()()"]<br>
示例 2：</p>
<p>输入：n = 1<br>
输出：["()"]</p>
<p>提示：</p>
<p>1 <= n <= 8</p>
<pre data-role="codeBlock" data-info="cpp" class="language-cpp"><span class="token keyword keyword-class">class</span> <span class="token class-name">Solution</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-public">public</span><span class="token operator">:</span>
vector<span class="token operator"><</span>string<span class="token operator">></span> <span class="token function">generateParenthesis</span><span class="token punctuation">(</span><span class="token keyword keyword-int">int</span> n<span class="token punctuation">)</span> <span class="token punctuation">{</span>
std<span class="token double-colon punctuation">::</span>vector<span class="token operator"><</span>std<span class="token double-colon punctuation">::</span>string<span class="token operator">></span> res<span class="token punctuation">;</span>
std<span class="token double-colon punctuation">::</span>string cur <span class="token operator">=</span> <span class="token string">""</span><span class="token punctuation">;</span>
<span class="token function">backtracking</span><span class="token punctuation">(</span>res<span class="token punctuation">,</span> n<span class="token punctuation">,</span> n<span class="token punctuation">,</span> cur<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword keyword-return">return</span> res<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword keyword-private">private</span><span class="token operator">:</span>
<span class="token keyword keyword-void">void</span> <span class="token function">backtracking</span><span class="token punctuation">(</span>std<span class="token double-colon punctuation">::</span>vector<span class="token operator"><</span>std<span class="token double-colon punctuation">::</span>string<span class="token operator">></span><span class="token operator">&</span> res<span class="token punctuation">,</span> <span class="token keyword keyword-int">int</span> left<span class="token punctuation">,</span> <span class="token keyword keyword-int">int</span> right<span class="token punctuation">,</span> std<span class="token double-colon punctuation">::</span>string<span class="token operator">&</span> cur<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>left <span class="token operator">==</span> <span class="token number">0</span> <span class="token operator">&&</span> right <span class="token operator">==</span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
res<span class="token punctuation">.</span><span class="token function">push_back</span><span class="token punctuation">(</span>cur<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword keyword-return">return</span> <span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token comment">// add left</span>
cur <span class="token operator">+=</span> <span class="token string">'('</span><span class="token punctuation">;</span>
<span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>left <span class="token operator">></span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token function">backtracking</span><span class="token punctuation">(</span>res<span class="token punctuation">,</span> left <span class="token operator">-</span> <span class="token number">1</span><span class="token punctuation">,</span> right<span class="token punctuation">,</span> cur<span class="token punctuation">)</span><span class="token punctuation">;</span>
cur<span class="token punctuation">.</span><span class="token function">pop_back</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// add right</span>
cur <span class="token operator">+=</span> <span class="token string">')'</span><span class="token punctuation">;</span>
<span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>left <span class="token operator"><</span> right <span class="token operator">&&</span> right <span class="token operator">></span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token function">backtracking</span><span class="token punctuation">(</span>res<span class="token punctuation">,</span> left<span class="token punctuation">,</span> right <span class="token operator">-</span> <span class="token number">1</span><span class="token punctuation">,</span> cur<span class="token punctuation">)</span><span class="token punctuation">;</span>
cur<span class="token punctuation">.</span><span class="token function">pop_back</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</pre><ul>
<li>空间复杂度： 大约O(n)</li>
<li>时间复杂度： O((4^n) / √n)</li>
<li>解法： 回溯</li>
<li>标签： <code>字符串</code>, <code>动态规划</code>, <code>回溯</code></li>
<li>难度： 中等</li>
</ul>
<h1 class="mume-header" id="23-%E5%90%88%E5%B9%B6k%E4%B8%AA%E5%8D%87%E5%BA%8F%E9%93%BE%E8%A1%A8">23. 合并K个升序链表</h1>
<p>TODO:</p>
<h1 class="mume-header" id="26-%E5%88%A0%E9%99%A4%E6%9C%89%E5%BA%8F%E6%95%B0%E7%BB%84%E4%B8%AD%E7%9A%84%E9%87%8D%E5%A4%8D%E9%A1%B9">26. 删除有序数组中的重复项</h1>
<p>给你一个有序数组 nums ，请你 原地 删除重复出现的元素，使每个元素 只出现一次 ，返回删除后数组的新长度。</p>
<p>不要使用额外的数组空间，你必须在 原地 修改输入数组 并在使用 O(1) 额外空间的条件下完成。</p>
<p>提示：</p>
<p>0 <= nums.length <= 3 * 10^4<br>
-10^4 <= nums[i] <= 10^4<br>
nums 已按升序排列</p>
<pre data-role="codeBlock" data-info="cpp" class="language-cpp"><span class="token keyword keyword-class">class</span> <span class="token class-name">Solution</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-public">public</span><span class="token operator">:</span>
<span class="token keyword keyword-int">int</span> <span class="token function">removeDuplicates</span><span class="token punctuation">(</span>vector<span class="token operator"><</span><span class="token keyword keyword-int">int</span><span class="token operator">></span><span class="token operator">&</span> nums<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>nums<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">==</span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token keyword keyword-return">return</span> <span class="token number">0</span><span class="token punctuation">;</span>
<span class="token keyword keyword-int">int</span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span>
<span class="token keyword keyword-for">for</span> <span class="token punctuation">(</span><span class="token keyword keyword-int">int</span> j <span class="token operator">=</span> <span class="token number">1</span><span class="token punctuation">;</span> j <span class="token operator"><</span> nums<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token operator">++</span>j<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>nums<span class="token punctuation">[</span>j<span class="token punctuation">]</span> <span class="token operator">!=</span> nums<span class="token punctuation">[</span>j <span class="token operator">-</span> <span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
i<span class="token operator">++</span><span class="token punctuation">;</span>
nums<span class="token punctuation">[</span>i<span class="token punctuation">]</span> <span class="token operator">=</span> nums<span class="token punctuation">[</span>j<span class="token punctuation">]</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span class="token keyword keyword-return">return</span> i <span class="token operator">+</span> <span class="token number">1</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</pre><ul>
<li>空间复杂度： O(1)</li>
<li>时间复杂度： O(n)</li>
<li>解法： 双指针</li>
<li>标签： <code>数组</code>, <code>双指针</code></li>
<li>难度： 简单</li>
</ul>
<h1 class="mume-header" id="28-%E5%AE%9E%E7%8E%B0-strstr">28. 实现 strStr()</h1>
<p>实现 strStr() 函数。</p>
<p>给你两个字符串 haystack 和 needle ，请你在 haystack 字符串中找出 needle 字符串出现的第一个位置（下标从 0 开始）。如果不存在，则返回 -1 。</p>
<p>说明：</p>
<p>当 needle 是空字符串时，我们应当返回什么值呢？这是一个在面试中很好的问题。</p>
<p>对于本题而言，当 needle 是空字符串时我们应当返回 0 。这与 C 语言的 strstr() 以及 Java 的 indexOf() 定义相符。</p>
<pre data-role="codeBlock" data-info="cpp" class="language-cpp"><span class="token keyword keyword-class">class</span> <span class="token class-name">Solution</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-public">public</span><span class="token operator">:</span>
<span class="token keyword keyword-int">int</span> <span class="token function">strStr</span><span class="token punctuation">(</span>string haystack<span class="token punctuation">,</span> string needle<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-for">for</span> <span class="token punctuation">(</span><span class="token keyword keyword-int">int</span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> <span class="token punctuation">;</span> <span class="token operator">++</span>i<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-for">for</span> <span class="token punctuation">(</span><span class="token keyword keyword-int">int</span> j <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> <span class="token punctuation">;</span> <span class="token operator">++</span>j<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>j <span class="token operator">==</span> needle<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token keyword keyword-return">return</span> i<span class="token punctuation">;</span>
<span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>i <span class="token operator">+</span> j <span class="token operator">==</span> haystack<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token keyword keyword-return">return</span> <span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">;</span>
<span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>haystack<span class="token punctuation">[</span>i <span class="token operator">+</span> j<span class="token punctuation">]</span> <span class="token operator">!=</span> needle<span class="token punctuation">[</span>j<span class="token punctuation">]</span><span class="token punctuation">)</span> <span class="token keyword keyword-break">break</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</pre><p>FIXME: KMP 解法</p>
<ul>
<li>空间复杂度： O(1)</li>
<li>时间复杂度：</li>
<li>解法： 双指针</li>
<li>标签： <code>双指针</code>, <code>字符串</code>, <code>字符匹配</code></li>
<li>难度： 简单</li>
</ul>
<h1 class="mume-header" id="29-%E4%B8%A4%E6%95%B0%E7%9B%B8%E9%99%A4">29. 两数相除</h1>
<p>给定两个整数，被除数 dividend 和除数 divisor。将两数相除，要求不使用乘法、除法和 mod 运算符。</p>
<p>返回被除数 dividend 除以除数 divisor 得到的商。</p>
<p>整数除法的结果应当截去（truncate）其小数部分，例如：truncate(8.345) = 8 以及 truncate(-2.7335) = -2</p>
<pre data-role="codeBlock" data-info="cpp" class="language-cpp"><span class="token keyword keyword-class">class</span> <span class="token class-name">Solution</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-public">public</span><span class="token operator">:</span>
<span class="token keyword keyword-int">int</span> <span class="token function">divide</span><span class="token punctuation">(</span><span class="token keyword keyword-int">int</span> dividend<span class="token punctuation">,</span> <span class="token keyword keyword-int">int</span> divisor<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span>dividend <span class="token operator">==</span> std<span class="token double-colon punctuation">::</span><span class="token class-name">numeric_limits</span><span class="token operator"><</span><span class="token keyword keyword-int">int</span><span class="token operator">></span><span class="token double-colon punctuation">::</span><span class="token function">min</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">&&</span> divisor <span class="token operator">==</span> <span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">)</span> <span class="token keyword keyword-return">return</span> std<span class="token double-colon punctuation">::</span><span class="token class-name">numeric_limits</span><span class="token operator"><</span><span class="token keyword keyword-int">int</span><span class="token operator">></span><span class="token double-colon punctuation">::</span><span class="token function">max</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword keyword-long">long</span> <span class="token keyword keyword-int">int</span> dvd <span class="token operator">=</span> std<span class="token double-colon punctuation">::</span><span class="token function">labs</span><span class="token punctuation">(</span>dividend<span class="token punctuation">)</span><span class="token punctuation">,</span> dvs <span class="token operator">=</span> std<span class="token double-colon punctuation">::</span><span class="token function">labs</span><span class="token punctuation">(</span>divisor<span class="token punctuation">)</span><span class="token punctuation">,</span> res <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span>
<span class="token keyword keyword-while">while</span> <span class="token punctuation">(</span>dvd <span class="token operator">>=</span> dvs<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword keyword-long">long</span> <span class="token keyword keyword-int">int</span> tmp <span class="token operator">=</span> dvs<span class="token punctuation">,</span> m <span class="token operator">=</span> <span class="token number">1</span><span class="token punctuation">;</span>
<span class="token keyword keyword-while">while</span> <span class="token punctuation">(</span>tmp <span class="token operator"><<</span> <span class="token number">1</span> <span class="token operator"><=</span> dvd<span class="token punctuation">)</span> <span class="token punctuation">{</span>
tmp <span class="token operator"><<=</span> <span class="token number">1</span><span class="token punctuation">;</span>
m <span class="token operator"><<=</span> <span class="token number">1</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
dvd <span class="token operator">-=</span> tmp<span class="token punctuation">;</span>
res <span class="token operator">+=</span> m<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword keyword-return">return</span> <span class="token punctuation">(</span>dividend <span class="token operator">></span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token operator">==</span> <span class="token punctuation">(</span>divisor <span class="token operator">></span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token operator">?</span> res <span class="token operator">:</span> <span class="token operator">-</span>res<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</pre><ul>
<li>空间复杂度：</li>
<li>时间复杂度：</li>
<li>解法：</li>
<li>标签： <code>位运算</code>, <code>数学</code></li>
<li>难度： 中等</li>
</ul>
<h1 class="mume-header" id="34-%E5%9C%A8%E6%8E%92%E5%BA%8F%E6%95%B0%E7%BB%84%E4%B8%AD%E6%9F%A5%E6%89%BE%E5%85%83%E7%B4%A0%E7%9A%84%E7%AC%AC%E4%B8%80%E4%B8%AA%E5%92%8C%E6%9C%80%E5%90%8E%E4%B8%80%E4%B8%AA%E4%BD%8D%E7%BD%AE">34. 在排序数组中查找元素的第一个和最后一个位置</h1>
<p>给定一个按照升序排列的整数数组 nums，和一个目标值 target。找出给定目标值在数组中的开始位置和结束位置。</p>
<p>如果数组中不存在目标值 target，返回 [-1, -1]。</p>
<p>进阶：</p>
<p>你可以设计并实现时间复杂度为 O(log n) 的算法解决此问题吗？</p>
<p>示例 1：</p>
<p>输入：nums = [5,7,7,8,8,10], target = 8<br>
输出：[3,4]<br>