| 3. Longest Substring Without Repeating Characters | Solution | Solve | Medium | | |
| 5. Longest Palindromic Substring | Solution | Solve | Medium | | |
| 7. Reverse Integer | Solution | Solve | Medium | | |
| 12. Integer to Roman | Solution | Solve | Medium | | |
| 17. Letter Combinations of a Phone Number | Solution | Solve | Medium | | |
| 18. 4Sum | Solution | Solve | Medium | | |
| 33. Search in Rotated Sorted Array | Solution | Solve | Medium | | |
| 34. Find First and Last Position of Element in Sorted Array | Solution | Solve | Medium | | |
| 36. Valid Sudoku | Solution | Solve | Medium | | |
| 39. Combination Sum | Solution | Solve | Medium | | |
| 40. Combination Sum II | Solution | Solve | Medium | | |
| 46. Permutations | Solution | Solve | Medium | | |
| 47. Permutations II | Solution | Solve | Medium | | |
| 50. Pow(x, n) | Solution | Solve | Medium | | |
| 53. Maximum Subarray | Solution | Solve | Medium | | |
| 56. Merge Intervals | Solution | Solve | Medium | | |
| 57. Insert Interval | Solution | Solve | Medium | | |
| 61. Rotate List | Solution | Solve | Medium | | |
| 62. Unique Paths | Solution | Solve | Medium | | |
| 72. Edit Distance | Solution | Solve | Medium | | |
| 79. Word Search | Solution | Solve | Medium | | |
| 98. Validate Binary Search Tree | Solution | Solve | Medium | | |
| 102. Binary Tree Level Order Traversal | Solution | Solve | Medium | | |
| 103. Binary Tree Zigzag Level Order Traversal | Solution | Solve | Medium | | |
| 128. Longest Consecutive Sequence | Solution | Solve | Medium | | |
| 139. Word Break | Solution | Solve | Medium | | |
| 143. Reorder List | Solution | Solve | Medium | | |
| 146. LRU Cache | Solution | Solve | Medium | | |
| 150. Evaluate Reverse Polish Notation | Solution | Solve | Medium | | |
| 151. Reverse Words in a String | Solution | Solve | Medium | | |
| 152. Maximum Product Subarray | Solution | Solve | Medium | | |
| 153. Find Minimum in Rotated Sorted Array | Solution | Solve | Medium | | |
| 155. Min Stack | Solution | Solve | Medium | | |
| 156. Binary Tree Upside Down | Solution | Solve | Medium | | |
| 173. Binary Search Tree Iterator | Solution | Solve | Medium | | |
| 187. Repeated DNA Sequences | Solution | Solve | Medium | | |
| 198. House Robber | Solution | Solve | Medium | | |
| 200. Number of Islands | Solution | Solve | Medium | | |
| 207. Course Schedule | Solution | Solve | Medium | | |
| 210. Course Schedule II | Solution | Solve | Medium | | |
| 211. Design Add and Search Words Data Structure | Solution | Solve | Medium | | |
| 213. House Robber II | Solution | Solve | Medium | | |
| 215. Kth Largest Element in an Array | Solution | Solve | Medium | | |
| 230. Kth Smallest Element in a BST | Solution | Solve | Medium | | |
| 235. Lowest Common Ancestor of a Binary Search Tree | Solution | Solve | Medium | | |
| 236. Lowest Common Ancestor of a Binary Tree | Solution | Solve | Medium | | |
| 238. Product of Array Except Self | Solution | Solve | Medium | | |
| 244. Shortest Word Distance II | Solution | Solve | Medium | | |
| 245. Shortest Word Distance III | Solution | Solve | Medium | | |
| 254. Factor Combinations | Solution | Solve | Medium | | |
