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"For coding interview preparation, LeetCode is one of the best online resource providing a rich library of more than 300 real coding interview questions for you to practice from using one of the 7 supported languages - C, C++, Java, Python, C#, JavaScript, Ruby."

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Contributing

Your ideas/fixes/algorithms are more than welcome!

1. Fork this repo
2. Create your feature branch (`git checkout -b my-awesome-feature`)
3. Commit your changes (`git commit -am 'Added some awesome feature'`)
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Algorithms

# Title Solutions Time Space Difficulty Tag Notes
594 Longest Harmonious Subsequence Solution O(n) O(n) Easy Array, HashMap
593 Valid Square Solution O(1) O(1) Medium Math
592 Fraction Addition and Subtraction Solution O(nlogx) O(n) Medium Math
588 Design In-Memory File System Solution O(n) O(h) Hard Trie, Design
583 Delete Operation for Two Strings Solution O(m*n) O(m*n) could be optimized to O(n) Medium DP
582 Kill Process Solution O(n) O(h) Medium Stack
581 Shortest Unsorted Continuous Subarray Solution O(n) O(1) Easy Array, Sort
575 Distribute Candies Solution O(nlogn) O(1) Easy Array
572 Subtree of Another Tree Solution O(m*n) O(1) Easy Tree
567 Permutation in String Solution O(max(m,n)) O(1) Medium Sliding Windows, Two Pointers
566 Reshape the Matrix Solution O(m*n) O(1) Easy
563 Binary Tree Tilt Solution O(n) O(n) Easy Tree Recursion
562 Longest Line of Consecutive One in Matrix Solution O(m*n) O(m*n) Medium Matrix DP
561 Array Partition I Solution O(nlogn) O(1) Easy Array
560 Subarray Sum Equals K Solution O(n) O(n) Medium Array, HashMap
557 Reverse Words in a String III Solution O(n) O(n) Easy String
556 Next Greater Element III Solution O(n) O(1) Medium String
555 Split Concatenated Strings Solution O(n^2) O(n) Medium String
554 Brick Wall Solution O(n) (n is total number of bricks in the wall) O(m) (m is width of the wall) Medium HashMap
551 Student Attendance Record I Solution O(n) O(1) Easy String
549 Binary Tree Longest Consecutive Sequence II Solution O(n) O(n) Medium Tree
548 Split Array with Equal Sum Solution O(n^2) O(1) Medium Array
547 Friend Circles Solution O(n^2) O(n) Medium Union Find
545 Boundary of Binary Tree Solution O(n) O(n) Medium Recursion
544 Output Contest Matches Solution O(n) O(n) Medium Recursion
543 Diameter of Binary Tree Solution O(n) O(h) Easy Tree/DFS/Recursion
542 01 Matrix Solution O(m*n) O(n) Medium BFS
541 Reverse String II Solution O(n) O(1) Easy String
540 Single Element in a Sorted Array Solution O(n) O(1) Medium
539 Minimum Time Difference Solution O(n) O(1) Medium String
538 Convert BST to Greater Tree Solution O(nlogn) O(n) Medium Tree
537 Complex Number Multiplication Solution O(1) O(1) Medium Math, String
536 Construct Binary Tree from String Solution O(n) O(h) Medium Recursion
535 Encode and Decode TinyURL Solution O(1) O(n) Medium Design
532 K-diff Pairs in an Array Solution O(n) O(n) Easy HashMap
531 Lonely Pixel I Solution O(m*n) O(1) Medium
530 Minimum Absolute Difference in BST Solution O(n) O(n) Easy DFS
529 Minesweeper Solution O(m*n) O(k) Medium BFS
526 Beautiful Arrangement Solution O(n) O(h) Medium Backtracking
525 Contiguous Array Solution O(n) O(n) Medium HashMap
524 Longest Word in Dictionary through Deleting Solution O(n) O(n) Medium Sort
523 Continuous Subarray Sum Solution O(n^2) O(n) Medium
522 Longest Uncommon Subsequence II Solution O(x*n^2) (x is average length of strings) O(1) Medium
521 Longest Uncommon Subsequence I Solution O(max(x,y)) (x and y are length of strings) O(1) Easy
520 Detect Capital Solution O(n) O(1) Easy
515 Find Largest Value in Each Tree Row Solution O(n) O(k) Medium BFS
513 Find Bottom Left Tree Value Solution O(n) O(k) Medium BFS
508 Most Frequent Subtree Sum Solution O(n) O(n) Medium DFS, Tree
507 Perfect Number Solution O(sqrt(n)) O(1) Easy Math
506 Relative Ranks Solution O(nlogn) O(n) Easy
505 The Maze II Solution O(m*n) O(m*n) Medium BFS
504 Base 7 Solution O(1) O(1) Easy
503 Next Greater Element II Solution O(n) O(n) Medium Stack
501 Find Mode in Binary Tree Solution O(n) O(k) Easy Binary Tree
500 Keyboard Row Solution O(n) O(1) Easy
499 The Maze III Solution O(m*n) O(m*n) Hard BFS
496 Next Greater Element I Solution O(n*m) O(1) Easy
495 Teemo Attacking Solution O(n) O(1) Medium Array
494 Target Sum Solution O(2^n) O(1) Medium
492 Construct the Rectangle Solution O(n) O(1) Easy Array
490 The Maze Solution O(m*n) O(m*n) Medium BFS
487 Max Consecutive Ones II Solution O(n) O(n) Medium Array
485 Max Consecutive Ones Solution O(n) O(1) Easy Array
484 Find Permutation Solution O(n) O(1) Medium Array, String, Greedy
482 License Key Formatting Solution O(n) O(n) Medium
477 Total Hamming Distance Solution O(n) O(1) Medium Bit Manipulation
476 Number Complement Solution O(n) O(1) Easy Bit Manipulation
475 Heaters Solution max(O(nlogn), O(mlogn)) - m is the length of houses, n is the length of heaters O(1) Easy Array Binary Search
474 Ones and Zeroes Solution O(n) O(m*n) Medium DP
472 Concatenated Words Solution O(n^2) O(n) Hard Trie, DP, DFS
468 Validate IP Address Solution O(n^2) O(n) Hard Trie, DP, DFS
467 Unique Substrings in Wraparound String Solution O(n) O(1) Medium DP
463 Island Perimeter Solution O(m*n) O(1) Easy
462 Minimum Moves to Equal Array Elements II Solution O(nlogn) O(1) Medium
461 Hamming Distance Solution O(n) O(1) Easy
459 Repeated Substring Pattern Solution O(n) O(n) Easy KMP
458 Poor Pigs Solution O(1) O(1) Easy Math
456 132 Pattern Solution O(n) O(n) Medium Stack
455 Assign Cookies Solution O(n) O(1) Easy
454 4Sum II Solution O(n) O(n) Medium HashMap
453 Minimum Moves to Equal Array Elements Solution O(n) O(1) Easy
452 Minimum Number of Arrows to Burst Balloons Solution O(nlogn) O(1) Medium Array, Greedy
451 Sort Characters By Frequency Solution O(nlogn) O(n) Medium HashMap
449 Serialize and Deserialize BST Solution O(n) O(h) Medium BFS
448 Find All Numbers Disappeared in an Array Solution O(n) O(1) Easy Array, HashMap
447 Number of Boomerangs Solution O(n^2) O(n) Easy HashMap
445 Add Two Numbers II Solution O(max(m,n) O(max(m,n)) Medium Stack, LinkedList
442 Find All Duplicates in an Array Solution O(n) O(1) Medium Array
441 Arranging Coins Solution O(n) O(1) Easy
439 Ternary Expression Parser Solution O(n) O(n) Medium Stack
438 Find All Anagrams in a String Solution O(n) O(1) Easy
437 Path Sum III Solution O(n^2) O(n) Easy DFS, recursion
436 Find Right Interval Solution O(nlogn) O(n) Medium Binary Search
435 Non-overlapping Intervals Solution O(nlogn) O(1) Medium Greedy
434 Number of Segments in a String Solution O(n) O(1) Easy
424 Longest Repeating Character Replacement Solution O(n) O(1) Medium Sliding Window
423 Reconstruct Original Digits from English Solution O(n) O(1) Medium Math
422 Valid Word Square Solution O(n) O(1) Easy
421 Maximum XOR of Two Numbers in an Array Solution O(n) O(1) Medium Bit Manipulation, Trie
420 Strong Password Checker Solution ? ? Hard
419 Battleships in a Board Solution O(m*n) O(1) Medium DFS
417 Pacific Atlantic Water Flow Solution O(mnMax(m,n)) O(m*n) Medium DFS
415 Add Strings Solution O(n) O(1) Easy
414 Third Maximum Number Solution O(n) O(1) Easy
413 Arithmetic Slices Solution O(n) O(1) Medium DP
412 Fizz Buzz Solution O(n) O(1) Easy
408 Valid Word Abbreviation Solution O(n) O(1) Easy
405 Convert a Number to Hexadecimal Solution O(n) O(1) Easy
404 Sum of Left Leaves Solution O(n) O(h) Easy
401 Binary Watch Solution O(1) O(1) Easy
400 Nth Digit Solution O(n) O(1) Easy
398 Random Pick Index Solution Medium Reservoir Sampling
397 Integer Replacement Solution ? ? Easy BFS
396 Rotate Function Solution O(n^2) could be optimized to O(n) O(1) Easy
392 Is Subsequence Solution O(m*n) O(1) Medium Array, String
390 Elimination Game Solution O(logn) O(1) Medium
389 Find the Difference Solution O(n) O(1) Easy
388 Longest Absolute File Path Solution O(n) O(d) Medium Stack
387 First Unique Character in a String Solution O(n) O(n) Easy HashMap
386 Lexicographical Numbers Solution O(n) O(1) Medium
385 Mini Parser Solution O(n) O(h) Medium Stack
379 Design Phone Directory Solution O(1) O(n) Medium
377 Combination Sum IV Solution O(?) O(?) Medium
375 Guess Number Higher or Lower II Solution O(n^2) O(n^2) Medium DP
374 Guess Number Higher or Lower Solution O(logn) O(1) Easy Binary Search
373 Find K Pairs with Smallest Sums Solution O(?) O(?) Medium Heap
372 Super Pow Solution O(n) O(1) Medium Math
371 Sum of Two Integers Solution O(n) O(1) Easy
370 Range Addition Solution O(n+k) O(1) Medium
369 Plus One Linked List Solution O(n) O(1) Medium Linked List
367 Valid Perfect Square Solution O(n) O(1) Medium
366 Find Leaves of Binary Tree Solution O(n) O(h) Medium DFS
365 Water and Jug Problem Solution O(n) O(1) Medium Math
364 Nested List Weight Sum II Solution O(n) O(h) Medium DFS
362 Design Hit Counter Solution O(1) amortized O(k) Medium Design
361 Bomb Enemy Solution O(?) O(?) Medium
360 Sort Transformed Array Solution O(n) O(1) Medium Two Pointers, Math
359 Logger Rate Limiter Solution amortized O(1) O(k) Easy HashMap
357 Count Numbers with Unique Digits Solution O(?) O(?) Medium
355 Design Twitter Solution O(n) O(n) Medium Design, HashMap, Heap
353 Design Snake Game Solution O(?) O(?) Medium
351 Android Unlock Patterns Solution O(?) O(?) Medium
350 Intersection of Two Arrays II Solution O(m+n) O((m+n)) could be optimized Easy HashMap, Binary Search
349 Intersection of Two Arrays Solution O(m+n) O(min(m,n)) Easy Two Pointers, Binary Search
348 Design Tic-Tac-Toe Solution O(1) O(n) Medium Design
346 Moving Average from Data Stream Solution O(1) O(w)) Easy Queue
344 Reverse String Solution O(n) O(1) Easy String
343 Integer Break Solution O(1) O(1) Medium Math
341 Flatten Nested List Iterator Solution O(n) O(n) Medium Stack
339 Nested List Weight Sum Solution O(n) O(h)) Easy DFS
338 Counting Bits Solution O(nlogn) O(h) Medium
337 House Robber III Solution O(n) O(n) Medium DP
336 Palindrome Pairs Solution O(n^2) O(n) Hard
334 Increasing Triplet Subsequence Solution O(n^2) O(1) Medium
333 Largest BST Subtree Solution O(n) O(n) Medium Tree
329 Longest Increasing Path in a Matrix Solution O(?) O(?) Hard
327 Count of Range Sum Solution O(?) O(?) Hard
325 Maximum Size Subarray Sum Equals k [Solution] O(n) O(n) Medium HashMap
323 Number of Connected Components in an Undirected Graph Solution O(?) O(?) Medium
322 Coin Change Solution O(?) O(?) Medium
321 Create Maximum Number Solution O(?) O(?) Hard
320 Generalized Abbreviation Solution O(n*2^n) O(n) Medium Backtracking, Bit Manipulation
317 Shortest Distance from All Buildings Solution O(?) O(?) Hard
315 Count of Smaller Numbers After Self Solution O(?) O(?) Hard Tree
314 Binary Tree Vertical Order Traversal Solution O(n) O(n) Medium HashMap, BFS
313 Super Ugly Number Solution O(?) O(?) Medium
312 Burst Balloons Solution O(?) O(?) Hard DP
311 Sparse Matrix Multiplication Solution O(mnl) O(m*l) Medium
310 Minimum Height Trees Solution ? ? Medium
309 Best Time to Buy and Sell Stock with Cooldown Solution O(n) O(1) Medium DP
308 Range Sum Query 2D - Mutable Solution ? ? Hard Tree
307 Range Sum Query - Mutable Solution ? ? Medium Tree
306 Additive Number Solution O(n^2) O(n) Medium
305 Number of Islands II Solution ? ? Hard Union Find
304 Range Sum Query 2D - Immutable Solution ? ? Medium
303 Range Sum Query - Immutable Solution O(n) O(1) Easy
302 Smallest Rectangle Enclosing Black Pixels Solution ? O(m*n) Hard DFS, BFS
301 Remove Invalid Parentheses Solution ? ? Hard BFS
300 Longest Increasing Subsequence Solution O(logn) O(n) Medium DP
299 Bulls and Cows Solution O(n) O(1) Easy
298 Binary Tree Longest Consecutive Sequence Solution O(n) O(n) Medium Tree
297 Serialize and Deserialize Binary Tree Solution O(n) O(h) Hard BFS
296 Best Meeting Point Solution ? ? Hard
295 Find Median from Data Stream Solution O(nlogn) O(n) Hard Heap
294 Flip Game II Solution ? ? Medium Backtracking
293 Flip Game Solution O(n) O(1) Easy
292 Nim Game Solution O(1) O(1) Easy
291 Word Pattern II Solution O(n) O(n) Hard
290 Word Pattern Solution O(n) O(n) Easy
289 Game of Life Solution O(m*n) O(m*n), could be optimized to O(1) Medium
288 Unique Word Abbreviation Solution O(n) O(1) Easy
287 Find the Duplicate Number Solution O(n) O(1) Medium
286 Walls and Gates Solution O(m*n) O(g) Medium BFS
285 Inorder Successor In BST Solution O(h) O(1) Medium Tree
284 Peeking Iterator Solution O(n) O(n) Medium Design
283 Move Zeroes Solution O(n) O(1) Easy
282 Expression Add Operators Solution O(?) O(?) Hard
281 Zigzag Iterator Solution O(n) O(n) Medium
280 Wiggle Sort Solution O(n) O(1) Medium
279 Perfect Squares Solution O(n) O(1) Medium
278 First Bad Version Solution O(logn) O(1) Easy Binary Search
277 Find the Celebrity Solution O(n) O(1) Medium
276 Paint Fence Solution O(n) O(1) Easy DP
274 H-Index Solution O(nlogn) O(1) Medium
273 Integer to English Words Solution O(n) O(1) Hard Math, String
272 Closest Binary Search Tree Value II Solution O(h+k) O(h) Hard Stack
271 Encode and Decode Strings Solution O(n) O(1) Medium
270 Closest Binary Search Tree Value Solution O(h) O(1) Easy DFS
268 Missing Number Solution O(n) O(1) Easy Bit Manipulation
267 Palindrome Permutation II Solution O(n*n!) O(n) Medium
266 Palindrome Permutation Solution O(n) O(1) Easy
265 Paint House II Solution ? ? Hard
263 Ugly Number Solution O(n) O(1) Easy
261 Graph Valid Tree Solution O(V+E) O(V+E) Medium
259 3Sum Smaller Solution O(n^2) O(1) Medium
258 Add Digits Solution O(1) O(1) Easy
257 Binary Tree Paths Solution O(n*h) O(h) DFS/Recursion
256 Paint House Solution O(n) O(1) Medium DP
255 Verify Preorder Sequence in Binary Search Tree Solution O(n) O(h) Medium Tree
254 Factor Combinations Solution O(nlogn) O(nlogn) Medium Backtracking
253 Meeting Rooms II Solution O(nlogn) O(h) Medium Heap
252 Meeting Rooms Solution O(nlogn) O(1) Easy
251 Flatten 2D Vector Solution O(1) O(m*n) Medium
250 Count Univalue Subtrees Solution O(n) O(h) Medium DFS
249 Group Shifted Strings Solution O(nlogn) O(n)
248 Strobogrammatic Number III Solution O(?) O(?) Hard
247 Strobogrammatic Number II Solution O(n^2) O(n) Medium Recursion
246 Strobogrammatic Number Solution O(n) O(1) Easy
245 Shortest Word Distance III Solution O(n) O(1) Medium
244 Shortest Word Distance II Solution O(n) O(n) Medium HashMap
243 Shortest Word Distance Solution O(n) O(1) Easy
242 Valid Anagram Solution O(n) O(1) Easy
240 Search a 2D Matrix II Solution O(log(m*n)) O(1) Medium Binary Search
239 Sliding Window Maximum Solution O(nlogn) O(k) Hard Heap
238 Product of Array Except Self Solution O(n) O(1) Medium Array
237 Delete Node in a Linked List Solution O(1) O(1) Easy LinkedList
236 Lowest Common Ancestor of a Binary Tree Solution O(n) O(h) Medium DFS
235 Lowest Common Ancestor of a Binary Search Tree Solution O(h) O(1) Easy DFS
233 Number of Digit One Solution O(n) O(1) Hard Math
232 Implement Queue using Stacks Solution O(n) O(n) Medium Stack, Design
230 Kth Smallest Element in a BST Solution O(n) O(k) Medium Tree
229 Majority Element II Solution O(n) O(n) Medium
228 Summary Ranges Solution O(n) O(1) Medium Array
226 Invert Binary Tree Solution O(n) O(h) Easy DFS, recursion
225 Implement Stack using Queues Solution O(n) O(n) Easy Stack, Queue
224 Basic Calculator Solution ? ? Hard
223 Rectangle Area Solution O(1) O(1) Easy
222 Count Complete Tree Nodes Solution O(?) O(h) Medium
220 Contains Duplicate III Solution O(nlogn) O(n) Medium TreeSet
219 Contains Duplicate II Solution O(n) O(n) Easy HashMap
218 The Skyline Problem Solution O(n) O(n) Hard TreeMap, Design
217 Contains Duplicate Solution O(n) O(n) Easy HashSet
215 Kth Largest Element in an Array Solution O(nlogn) O(n) Medium Heap
213 House Robber II Solution O(n) O(n) Medium DP
212 Word Search II Solution O(mnl) O(l) Hard Trie
211 Add and Search Word - Data structure design Solution O(n) O(h) Medium Trie
210 Course Schedule II Solution O(?) O(?) Medium
209 Minimum Size Subarray Sum Solution O(n) O(1) Medium
208 Implement Trie Solution O(n) O(1) Medium Trie
207 Course Schedule Solution O(?) O(?) Medium
206 Reverse Linked List Solution O(n) O(1) Easy
205 Isomorphic Strings Solution O(n) O(1) Easy
204 Count Primes Solution O(sqrt(n)) O(n) Easy
202 Happy Number Solution O(k) O(k) Easy
201 Bitwise AND of Numbers Range Solution O(min(m,n)) O(1) Medium Bit Manipulation
200 Number of Islands Union Find DFS O(m*n) O(m*n) Medium Union Find, DFS
198 House Robber Solution O(n) O(n) Easy DP
191 Number of 1 Bits Solution O(n) O(1) Easy Bit Manipulation
190 Reverse Bits Solution O(n) O(1) Easy Bit Manipulation
189 Rotate Array Solution O(n) O(n), could be optimized to O(1) Easy
187 Repeated DNA Sequences Solution O(n) O(n) Medium
186 Reverse Words in a String II Solution O(n) O(1) Medium
179 Largest Number Queue Stack O(?) O(?) Medium
174 Dungeon Game Queue Stack O(m*n) O(m*n) Hard DP
173 Binary Search Tree Iterator Queue Stack O(1) O(h) Medium Stack, Design
172 Factorial Trailing Zeroes Solution O(logn) O(1) Easy
171 Excel Sheet Column Number Solution O(n) O(1) Easy
170 Two Sum III - Data structure design Solution O(n) O(n) Easy
169 Majority Element Solution O(n) O(1) Easy
168 Excel Sheet Column Title Solution O(n) O(1) Easy
167 Two Sum II - Input array is sorted Solution O(logn) O(1) Easy
165 Compare Version Numbers Solution O(n) O(1) Easy
164 Maximum Gap Solution O(n) O(n) Hard
163 Missing Ranges Solution O(n) O(1)
162 Find Peak Element Solution O(1) O(logn)/O(n) Binary Search
161 One Edit Distance Solution O(n) O(1)
160 Intersection of Two Linked Lists Solution O(m+n) O(1) Easy Linked List
159 Longest Substring with At Most Two Distinct Characters Solution O(n) O(1) Hard String, Sliding Window
158 Read N Characters Given Read4 II - Call multiple times Solution O(n) O(1) Hard
157 Read N Characters Given Read4 Solution O(n) O(1) Easy
156 Binary Tree Upside Down Solution O(n) O(h) Medium Tree, Recursion
155 Min Stack Solution O(1) O(n) Easy Stack
153 Find Minimum in Rotated Sorted Array Solution O(logn) O(1) Medium Array, Binary Search
152 Maximum Product Subarray Solution O(n) O(1) Medium Array
151 Reverse Words in a String Solution O(n) O(n) Medium
150 Evaluate Reverse Polish Notation Solution O(?) O(?) Medium
149 Max Points on a Line Solution O(?) O(?) Hard
147 Insertion Sort List Solution O(n^2) O(1) Medium Linked List
146 LRU Cache Doubly Linked List Linked Hash Map O(?) O(?) Hard Linked List
145 Binary Tree Postorder Traversal Solution O(n) O(h) Hard Binary Tree
144 Binary Tree Preorder Traversal Solution O(n) O(h) Medium Binary Tree
143 Reorder List Solution O(n) O(1) Medium
142 Linked List Cycle II Solution O(n) O(1) Medium Linked List
141 Linked List Cycle Solution O(n) O(1) Easy Linked List
140 Word Break II Solution ? O(n^2) Hard Backtracking/DFS
139 Word Break Solution O(n^2) O(n) Medium DP
138 Copy List with Random Pointer Solution O(n) O(n) Medium LinkedList, HashMap
137 Single Number II Solution O(n) O(n) Medium
135 Candy Solution O(n) O(1) Hard Greedy
133 Clone Graph Solution O(n) O(n) Medium HashMap, BFS, Graph
132 Implement Queue using Stacks Solution O(n) O(n) Easy Stack, Queue
130 Surrounded Regions Solution O(?) O(?) Medium
129 Sum Root to Leaf Numbers Solution O(n) O(h) Medium DFS
125 Valid Palindrome Solution O(n) O(1) Easy Two Pointers
124 Binary Tree Maximum Path Sum Solution O(n) O(h) Hard Tree, DFS
123 Best Time to Buy and Sell Stock III Solution O(?) O(?) Hard
122 Best Time to Buy and Sell Stock II Solution O(n) O(1) Medium Greedy
121 Best Time to Buy and Sell Stock Solution O(n) O(1) Easy DP
120 Triangle Solution O(m*n) O(n) Medium DP
119 Pascal's Triangle II Solution O(n^2) O(1) Easy
118 Pascal's Triangle Solution O(n^2) O(1) Easy
117 Populating Next Right Pointers in Each Node II Solution O(n) O(1) Medium BFS
116 Populating Next Right Pointers in Each Node Solution O(n) O(1) Medium BFS
115 Distinct Subsequences Solution O(m*n) O(m*n) Hard DP
114 Flatten Binary Tree to Linked List Solution O(n) O(h) Medium Tree
112 Path Sum Solution O(n) O(1) Easy DFS
111 Minimum Depth of Binary Tree Solution O(n) O(1)~O(h) Easy BFS, DFS
110 Balanced Binary Tree Solution O(n) O(1)~O(h) Easy DFS
109 Convert Sorted List to Binary Search Tree Solution O(n) O(h) Medium DFS, Recursion
108 Convert Sorted Array to Binary Search Tree Solution O(n) O(h) Medium Tree
107 Binary Tree Level Order Traversal II Solution O(nlogn) O(h) Easy BFS
106 Construct Binary Tree from Inorder and Postorder Traversal Solution O(n) O(n) Medium Recursion, Tree
105 Construct Binary Tree from Preorder and Inorder Traversal Solution O(n) O(n) Medium Recursion, Tree
104 Maximum Depth of Binary Tree Solution O(n) O(h) Easy DFS
103 Binary Tree Zigzag Level Order Traversal Solution O(n) O(h) Medium BFS,DFS
102 Binary Tree Level Order Traversal Solution O(n) O(h) Medium BFS
101 Symmetric Tree Solution O(n) O(h) Easy DFS
99 Recover Binary Search Tree Solution O(?) O(?) Hard
98 Validate Binary Search Tree Solution O(n) O(h) Medium DFS/Recursion
97 Interleaving String Solution O(?) O(?) Hard DP
96 Unique Binary Search Trees Solution O(n^2) O(n) Medium Recursion, DP
95 Unique Binary Search Trees II Solution O(?) O(?) Medium Recursion
94 Binary Tree Inorder Traversal Solution O(n) O(h) Medium Binary Tree
93 Restore IP Addresses Solution O(1) O(1) Medium Backtracking
92 Reverse Linked List II Solution O(n) O(1) Medium
91 Decode Ways Solution O(n) O(n) Medium DP
89 Gray Code Solution O(n) O(1) Medium Bit Manipulation
88 Merge Sorted Array Solution O(max(m,n)) O(1) Easy
86 Partition List Solution O(?) O(?) Medium
85 Maximal Rectangle Solution O(m*n) O(n) Hard DP
83 Remove Duplicates from Sorted List Solution O(n) O(1) Medium Linked List
82 Remove Duplicates from Sorted List II Solution O(n) O(1) Medium Linked List
81 Search in Rotated Sorted Array II Solution O(logn) O(1) Medium Binary Search
80 Remove Duplicates from Sorted Array II Solution O(n) O(n) Medium
79 Word Search Solution O(mnl) ? O(m*n) Medium Backtracking, DFS
78 Subsets Solution O(n^2) ? O(1) Medium Backtracking
76 Minimum Window Substring Solution O(n) O(k) Hard Two Pointers
75 Sort Colors Solution O(n) O(1) Medium Two Pointers
74 Search a 2D Matrix Solution O(logn) O(1) Medium Binary Search
73 Set Matrix Zeroes Solution O(mn) O(mn) Medium
72 Edit Distance Solution O(m*n) O(m+n) Hard
71 Simplify Path Solution O(n) O(n) Medium Stack
70 Climbing Stairs Solution O(n) O(n) Easy DP
69 Sqrt(x) Solution O(logn) O(1) Easy
68 Text Justification Solution O(n) O(1) Hard
67 Add Binary Solution O(n) O(1) Easy
66 Plus One Solution O(n) O(1) Easy
65 Valid Number Solution O(n) O(1) Hard
64 Minimum Path Sum Solution O(m*n) O(m*n) Medium DP
63 Unique Paths II Solution O(m*n) O(m*n) Medium DP
61 Rotate List Solution O(n) O(1) Medium Linked List
60 Permutation Sequence Solution ? ? Medium
59 Spiral Matrix II Solution O(n) O(n) Medium
58 Length of Last Word Solution O(n) O(1) Easy
56 Merge Intervals Solution O(n*logn) O(1) Medium Array, Sort
55 Jump Game Solution O(n) O(1) Medium Greedy
54 Spiral Matrix Solution O(m*n) O(m*n) Medium Array
53 Maximum Subarray Solution O(n) O(1) Easy
50 Pow(x, n) Solution O(logn) O(logn) Medium
48 Rotate Image Solution O(n^2) O(1) Medium Array
47 Permutations II Solution O(n*n!) O(n) Medium Backtracking
46 Permutations Solution O(n*n!) O(n) Medium Backtracking
45 Jump Game II Solution O(?) O(?) Hard
42 Trapping Rain Water Solution O(n) O(1) Hard
41 First Missing Positive Solution O(n) O(1) Hard
40 Combination Sum II Solution O(k*n^k) O(k) Medium Backtracking
39 Combination Sum Solution O(k*n^k) O(k) Medium Backtracking
38 Count and Say Solution O(n*2^n) O(2^n) Easy Recursion, LinkedList
37 Sudoku Solver Solution O((9!)^9) O(1) Hard
36 Valid Sudoku Solution O(1) O(1) Medium
35 Search Insert Position Solution O(n) O(1) Medium Array
34 Search for a Range Solution O(logn) O(1) Medium Array, Binary Search
33 Search in Rotated Sorted Array Solution O(logn) O(1) Medium Binary Search
32 Longest Valid Parentheses Solution O(n) O(n) Hard Stack, DP
31 Next Permutation Solution O(n) O(1) Medium Array
30 Substring with Concatenation of All Words Solution O(n^2) O(n) Hard HashMap
29 Divide Two Integers Solution O(?) O(?) Medium
28 Implement strStr() Solution O(n) O(1) Easy String
27 Remove Element Solution O(n) O(1) Easy
26 Remove Duplicates from Sorted Array Solution O(n) O(1) Easy Array
25 Reverse Nodes in k-Group Solution O(n) O(1) Hard Recursion, LinkedList
24 Swap Nodes in Pairs Solution O(n) O(h) Medium Recursion, LinkedList
23 Merge k Sorted Lists Solution O(n*logk) O(logk) Hard Heap
22 Generate Parentheses Solution TBD O(n) Medium Backtracking
21 Merge Two Sorted Lists Solution O(n) O(h) Easy Recursion
20 Valid Parentheses Solution O(n) O(n) Easy Stack
19 Remove Nth Node From End of List Solution O(n) O(1) Medium Linked List
18 4 Sum Solution O(n^2) O(1) Medium Two Pointers
17 Letter Combinations of a Phone Number Solution O(n*4^n) O(n) Medium Backtracking
16 3Sum Closest Solution O(nlogn) O(1) Medium Two Pointers
15 3Sum Solution O(n^2) O(1) Medium Two Pointers
14 Longest Common Prefix Solution O(n*min(wordLength in this array)) O(1) Easy
13 Roman to Integer Solution O(1) O(1) Easy
12 Integer to Roman Solution O(1) O(1) Medium
11 Container With Most Water Solution O(n) O(1) Medium
10 Regular Expression Matching Solution O(m*n) O(m*n) Hard DP
9 Palindrome Number Solution O(logn)/(n) O(1) Easy
8 String to Integer (atoi) Solution O(n) O(1) Medium
7 Reverse Integer Solution O(1) O(1) Easy
6 ZigZag Conversion Solution O(n) O(n) Easy
5 Longest Palindromic Substring Solution O(n^2) O(1) Medium
4 Median of Two Sorted Arrays Solution ? ? Hard Divide and Conquer
3 Longest Substring Without Repeating Characters Solution O(n) O(1) Medium HashMap, Sliding Window
2 Add Two Numbers Solution O(max(m,n)) O(1) Medium LinkedList
1 Two Sum Solution O(n)/O(n^2) O(1)/O(n) Easy HashMap

Database

# Title Solutions Time Space Difficulty Tag Notes
197 Rising Temperature Solution O(n^2) O(n) Easy
196 Delete Duplicate Emails Solution O(n^2) O(n) Easy
184 Department Highest Salary Solution O(n^2) O(n) Medium
183 Customers Who Never Order Solution O(n^2) O(n) Easy
182 Duplicate Emails Solution O(n^2) O(n) Easy
181 Employees Earning More Than Their Managers Solution O(n^2) O(n) Easy
180 Consecutive Numbers Solution O(n) O(n) Medium
178 Rank Scores Solution ? ? Medium
177 Nth Highest Salary Solution O(n) O(1) Medium
176 Second Highest Salary Solution O(n) O(1) Easy
175 Combine Two Tables Solution O(m+n) O(m+n) Easy

Shell

# Title Solutions Time Space Difficulty Tag Notes
195 Tenth Line Solution O(n) O(1) Easy
194 Transpose File Solution O(n^2) O(n^2) Medium
193 Valid Phone Numbers Solution O(n) O(1) Easy
192 Word Frequency Solution O(n) O(k) Medium

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