The Python 3 journey of leetcode Problems Algorithms
You may meet some problems on the way, and it(Problems you may face to) may be helpful.
Here is the classification of free questions.
- Array
- Hash Table
- Linked List
- Math
- Two Pointers
- String
- Binary Search
- Divide & Conquer
- Backtracking
- Dynamic Programming
- Stack
- Heap
- Greedy
- Sort
| No. | Title | Difficulty | Time | Space | Solution Runtime | Tip |
|---|---|---|---|---|---|---|
| 1 | Two Sum | Easy | O(n) | O(n) | 85.53(42ms,170626) | set |
| 3 | Longest Substring Without Repeating Characters | Medium | O(n) | O(n) | 88.87(89ms, 1704) | between the same |
| 18 | 4Sum | Medium | O(n^3) | O(1) | 86.12(132ms, 1703) | 3sum |
| 30 | Substring with Concatenation of All Words | Hard | O(mnk) | O(nk) | 70.72(98ms,170620) | use find info |
| 36 | Valid Sudoku | Medium | O(9×9) | O(9×9) | 75.42(76ms,170623) | many ways to check |
| 37 | Sudoku Solver | Hard | O((9!)^9) | O(1) | 90.91(72ms,170623) | check then put, if wrong backtrack. Or play like human |
| 49 | Group Anagrams | Medium | O(mn) | O(mn) | 90.95(212ms,170711) | frequency with hash |
| No. | Title | Difficulty | Time | Space | Solution Runtime | Tip |
|---|---|---|---|---|---|---|
| 2 | Add Two Numbers | Medium | O(n) | O(1) | 61.77(135ms,1704) | |
| 19 | Remove Nth Node From End of List | Easy | O(n) | O(1) | 93.74(42ms,170623) | |
| 21 | Merge Two Sorted Lists | Easy | O(n) | O(1) | 73.67(52ms, 1705) | |
| 23 | Merge k Sorted Lists | Hard | O(nlogk) | O(1) | 98.15(105ms, 1703) | |
| 24 | Swap Nodes in Pairs | Easy | O(n) | O(1) | 60.77(42ms, 1703) | |
| 25 | Reverse Nodes in k-Group | Hard | O(n) | O(1) | 73.50(72ms,170605) | |
| 61 | Rotate List | Medium | O(n) | O(1) | 83.99(45ms,170811) |
| No. | Title | Difficulty | Time | Space | Solution Runtime | Tip |
|---|---|---|---|---|---|---|
| 2 | Add Two Numbers | Medium | O(n) | O(1) | 61.77(135ms,1704) | |
| 7 | Reverse Integer | Easy | O(n) | O(1) | 34.12(66ms, 1703) | |
| 8 | String to Integer (atoi) | Medium | O(n) | O(1) | 44.69(78ms, 1704) | |
| 9 | Palindrome Number | Easy | O(n) | O(1) | 80.74(216ms, 1704) | |
| 12 | Integer to Roman | Medium | O(n) | O(1) | 90.62(105ms, 1705) | directly |
| 13 | Roman to Integer | Medium | O(n) | O(1) | 88.58(132ms, 1705) | lambda |
| 29 | Divide Two Integers | Medium | O(m/n) | O(1) | 33.58(68ms, 1703) | |
| 43 | Multiply Strings | Medium | O(m*n) | O(m+n) | 94.76(49ms,1704) / 76.65(168ms,170629) | carry, once |
| 50 | Pow(x, n) | Medium | O(m*n) | O(m+n) | 74.33(39ms, 1705) | |
| 60 | Permutation Sequence | Medium | O(n) | O(n) | 33.52(45ms, 1705) | |
| 65 | Valid Number | Hard | O(1) | O(1) | 37.72(62ms,170729) | |
| 66 | Plus One | Easy | O(n) | O(1) | 32.37(42ms,1705) | |
| 67 | Add Binary | Easy | O(1) | O(1) | 82.49(42ms,1705) | |
| 69 | Sqrt(x) | Easy | O(1) | O(1) | 77.55(42ms,1705) | sqrtx |
| No. | Title | Difficulty | Time | Space | Solution Runtime | Tip |
|---|---|---|---|---|---|---|
| 3 | Longest Substring Without Repeating Characters | Medium | O(n) | O(n) | 88.87(89ms, 1704) | between the same |
| 11 | Container With Most Water | Medium | O(n) | O(1) | 85.39(69ms, 1705) | from limit |
| 15 | 3Sum | Medium | O(n^2) | O(1) | 97.21(848ms, 1705) | sorted, meet |
| 16 | 3Sum Closest | Medium | O(n^2) | O(1) | 56.32(145ms, 1705) | sorted, meet |
| 18 | 4Sum | Medium | O(n^3) | O(1) | 86.12(132ms, 1703) | 3sum |
| 19 | Remove Nth Node From End of List | Medium | O(n) | O(1) | 93.74(42ms,170623) | |
| 26 | Remove Duplicates from Sorted Array | Easy | O(n) | O(1) | 77.68(79ms,170801) | |
| 27 | Remove Element | Easy | O(n) | O(1) | 67.84(45ms, 1703) | |
| 28 | Implement strStr() | Easy | O(mn) | O(n) | 41.03(58ms, 1703) | |
| 30 | Substring with Concatenation of All Words | Hard | O(mnk) | O(nk) | 70.72(98ms,170620) | use find info |
| 42 | Trapping Rain Water | Hard | O(n) | O(n) | 72.91(52ms,170627) | PEAK peak PEAK |
| 61 | Rotate List | Medium | O(n) | O(1) | 83.99(45ms,170811) |
| No. | Title | Difficulty | Time | Space | Solution Runtime | Tip |
|---|---|---|---|---|---|---|
| 4 | Median of Two Sorted Arrays | Hard | O(log(m+n)) | O(1) | 78.16(99ms, 1706) | find kth |
| 29 | Divide Two Integers | Medium | O(m/n) | O(1) | 33.58(68ms, 1703) | |
| 33 | Search in Rotated Sorted Array | Medium | O(logn) | O(1) | 21.87(58ms, 1703) | Binary Search |
| 34 | Search for a Range | Medium | O(logn) | O(1) | 73.72(45ms,170620) | Search left, then right |
| 35 | Search Insert Position | Easy | O(logn) | O(1) | 82.93(39ms,170620) | check range & bisect |
| 50 | Pow(x, n) | Medium | O(m*n) | O(m+n) | 74.33(39ms, 1705) | |
| 69 | Sqrt(x) | Easy | O(1) | O(1) | 77.55(42ms,1705) | sqrtx |
| No. | Title | Difficulty | Time | Space | Solution Runtime | Tip |
|---|---|---|---|---|---|---|
| 4 | Median of Two Sorted Arrays | Hard | O(log(m+n)) | O(1) | 78.16(99ms, 1706) | find kth |
| 23 | Merge k Sorted Lists | Hard | O(nlogk) | O(1) | 98.15(105ms, 1703) | |
| 53 | Maximum Subarray | Medium | O(n) | O(1) | 88.17(45ms,170719) |
| No. | Title | Difficulty | Time | Space | Solution Runtime | Tip |
|---|---|---|---|---|---|---|
| 10 | Regular Expression Matching | Hard | O(mn) | O(mn) | 85.45(82ms, 1705) | |
| 17 | Letter Combinations of a Phone Number | Medium | O(4^n) | O(n) | 62.18(42ms, 1705) | reduce works |
| 22 | Generate Parentheses | Medium | O(4^n / n^(3/2)) | O(n) | 28.90(65ms, 1703) | generate, closed? |
| 37 | Sudoku Solver | Hard | O((9!)^9) | O(1) | 90.91(72ms,170623) | check then put, if wrong backtracking. Or play like human |
| 39 | Combination Sum | Medium | O(k*n^k) | O(k^2) | 99.81(72ms,170625) | backtracking, check target |
| 40 | Combination Sum II | Medium | O(k*n^k) | O(k^2) | 93.17(65ms,170626) | |
| 44 | Wildcard Matching | Hard | O(m*n) | O(1) | 86.49(109ms,1704) | |
| 46 | Permutations | Medium | O(n!) | O(n*n!) | 87.53(66ms,1704) | |
| 47 | Permutations II | Medium | O(n!) | O(n*n!) | 94.36(99ms,1703) | |
| 51 | N-Queens | Hard | O(n^3) | O(n*n) | 100(62ms,170717) | bit |
| 52 | N-Queens II | Hard | O(n^3) | O(n*n) | 99.27(42ms, 1704) | bit |
| 60 | Permutation Sequence | Medium | O(n) | O(n) | 33.52(45ms, 1705) |
| No. | Title | Difficulty | Time | Space | Solution Runtime | Tip |
|---|---|---|---|---|---|---|
| 10 | Regular Expression Matching | Hard | O(mn) | O(mn) | 85.45(82ms, 1705) | |
| 32 | Longest Valid Parentheses | Hard | O(n) | O(1) | 72.88(79ms,170614) | |
| 44 | Wildcard Matching | Hard | O(m*n) | O(1) | 86.49(109ms,1704) | |
| 53 | Maximum Subarray | Medium | O(n) | O(1) | 88.17(45ms,170719) | |
| 62 | Unique Paths | Medium | O(1) | O(1) | 76.22(32ms,1705) | directly |
| 63 | Unique Paths II | Medium | O(mn) | O(m) | 51,91(39ms,170815) | |
| 64 | Minimum Path Sum | Medium | O(mn) | O(m) | 66.04(58ms,1705) | |
| 70 | Climbing Stairs | Easy | O(1) | O(1) | 38.2(36ms,1705) | |
| 72 | Edit Distance | Hard | O(mn) | O(n) | 91.79(198ms,17005) |
| No. | Title | Difficulty | Time | Space | Solution Runtime | Tip |
|---|---|---|---|---|---|---|
| 20 | Valid Parentheses | Easy | O(n) | O(n) | 92.77(39ms, 1703) | |
| 42 | Trapping Rain Water | Hard | O(n) | O(n) | 72.91(52ms,170627) | PEAK peak PEAK |
| 71 | Simplify Path | Medium | O(n) | O(n) | 67.63(42ms,170827) |
| No. | Title | Difficulty | Time | Space | Solution Runtime | Tip |
|---|---|---|---|---|---|---|
| 23 | Merge k Sorted Lists | Hard | O(nlogk) | O(1) | 98.15(105ms, 1703) | replace |
| No. | Title | Difficulty | Time | Space | Solution Runtime | Tip |
|---|---|---|---|---|---|---|
| 44 | Wildcard Matching | Hard | O(m*n) | O(1) | 86.49(109ms,1704) | |
| 45 | Jump Game II | Hard | O(n) | O(n) | 98.24(49ms,170705) | |
| 55 | Jump Game | Medium | O(m) | O(1) | 63.92(52ms,170723) |
| No. | Title | Difficulty | Time | Space | Solution Runtime | Tip |
|---|---|---|---|---|---|---|
| 56 | Merge Intervals | Medium | O(m) | O(1) | 92.09(72ms,170726) | |
| 57 | Insert Interval | Hard | O(m) | O(1) | 98.84(62ms,170727) | leetcode may give wrong Runtime |