| 1 | Two Sum | Easy | 1116 | arrayhash-table |
| 2 | Add Two Numbers | Medium | 1395 | linked-listmathrecursion |
| 3 | Longest Substring Without Repeating Characters | Medium | 1533 | hash-tablestringsliding-window |
| 4 | Median of Two Sorted Arrays | Hard | 2028 | arraybinary-searchdivide-and-conquer |
| 5 | Longest Palindromic Substring | Medium | 1581 | two-pointersstringdynamic-programming |
| 6 | Zigzag Conversion | Medium | 1568 | string |
| 7 | Reverse Integer | Medium | 1413 | math |
| 8 | String to Integer (atoi) | Medium | 1545 | string |
| 9 | Palindrome Number | Easy | 1168 | math |
| 10 | Regular Expression Matching | Hard | 2025 | stringdynamic-programmingrecursion |
| 11 | Container With Most Water | Medium | 1704 | arraytwo-pointersgreedy |
| 12 | Integer to Roman | Medium | 1433 | hash-tablemathstring |
| 13 | Roman to Integer | Easy | 1258 | hash-tablemathstring |
| 14 | Longest Common Prefix | Easy | 1170 | stringtrie |
| 15 | 3Sum | Medium | 1711 | arraytwo-pointerssorting |
| 16 | 3Sum Closest | Medium | 1502 | arraytwo-pointerssorting |
| 17 | Letter Combinations of a Phone Number | Medium | 1460 | hash-tablestringbacktracking |
| 18 | 4Sum | Medium | 1639 | arraytwo-pointerssorting |
| 19 | Remove Nth Node From End of List | Medium | 1474 | linked-listtwo-pointers |
| 20 | Valid Parentheses | Easy | 1211 | stringstack |
| 21 | Merge Two Sorted Lists | Easy | 1168 | linked-listrecursion |
| 22 | Generate Parentheses | Medium | 1648 | stringdynamic-programmingbacktracking |
| 23 | Merge K Sorted Lists | Hard | 1893 | linked-listdivide-and-conquerheap-priority-queue+1 |
| 24 | Swap Nodes in Pairs | Medium | 1408 | linked-listrecursion |
| 25 | Reverse Nodes in k-Group | Hard | 2011 | linked-listrecursion |
| 26 | Remove Duplicates from Sorted Array | Easy | 1169 | arraytwo-pointers |
| 27 | Remove Element | Easy | 1153 | arraytwo-pointers |
| 28 | Find the Index of the First Occurrence in a String | Easy | 1302 | two-pointersstringstring-matching |
| 29 | Divide Two Integers | Medium | 1645 | mathbit-manipulation |
| 30 | Substring with Concatenation of All Words | Hard | 2039 | hash-tablestringsliding-window |
| 31 | Next Permutation | Medium | 1560 | arraytwo-pointers |
| 32 | Longest Valid Parentheses | Hard | 2118 | stringdynamic-programmingstack |
| 33 | Search in Rotated Sorted Array | Medium | 1625 | arraybinary-search |
| 34 | Find First and Last Position of Element in Sorted Array | Medium | 1483 | arraybinary-search |
| 35 | Search Insert Position | Easy | 1164 | arraybinary-search |
| 36 | Valid Sudoku | Medium | 1422 | arrayhash-tablematrix |
| 37 | Sudoku Solver | Hard | 2313 | arrayhash-tablebacktracking+1 |
| 39 | Combination Sum | Medium | 1469 | arraybacktracking |
| 40 | Combination Sum II | Medium | 1562 | arraybacktracking |
| 41 | First Missing Positive | Hard | 1944 | arrayhash-table |
| 42 | Trapping Rain Water | Hard | 2062 | arraytwo-pointersdynamic-programming+2 |
| 43 | Multiply Strings | Medium | 1499 | mathstringsimulation |
| 44 | Wildcard Matching | Hard | 2100 | stringdynamic-programminggreedy+1 |
| 45 | Jump Game II | Medium | 1618 | arraydynamic-programminggreedy |
| 46 | Permutations | Medium | 1519 | arraybacktracking |
| 47 | Permutations II | Medium | 1574 | arraybacktracking |
| 48 | Rotate Image | Medium | 1407 | arraymathmatrix |
| 49 | Group Anagrams | Medium | 1474 | arrayhash-tablestring+1 |
| 50 | Pow(x, n) | Medium | 1460 | mathrecursion |
| 51 | N-Queens | Hard | 1797 | arraybacktracking |