| 4. Median of Two Sorted Arrays | Solution | Solve | Hard | | |
| 10. Regular Expression Matching | Solution | Solve | Hard | | |
| 23. Merge k Sorted Lists | Solution | Solve | Hard | | |
| 25. Reverse Nodes in k-Group | Solution | Solve | Hard | | |
| 30. Substring with Concatenation of All Words | Solution | Solve | Hard | | |
| 32. Longest Valid Parentheses | Solution | Solve | Hard | | |
| 37. Sudoku Solver | Solution | Solve | Hard | | |
| 41. First Missing Positive | Solution | Solve | Hard | | |
| 42. Trapping Rain Water | Solution | Solve | Hard | | |
| 44. Wildcard Matching | Solution | Solve | Hard | | |
| 51. N-Queens | Solution | Solve | Hard | | |
| 52. N-Queens II | Solution | Solve | Hard | | |
| 60. Permutation Sequence | Solution | Solve | Hard | | |
| 65. Valid Number | Solution | Solve | Hard | | |
| 68. Text Justification | Solution | Solve | Hard | | |
| 76. Minimum Window Substring | Solution | Solve | Hard | | |
| 84. Largest Rectangle in Histogram | Solution | Solve | Hard | | |
| 85. Maximal Rectangle | Solution | Solve | Hard | | |
| 115. Distinct Subsequences | Solution | Solve | Hard | | |
| 123. Best Time to Buy and Sell Stock III | Solution | Solve | Hard | | |
| 124. Binary Tree Maximum Path Sum | Solution | Solve | Hard | | |
| 126. Word Ladder II | Solution | Solve | Hard | | |
| 127. Word Ladder | Solution | Solve | Hard | | |
| 132. Palindrome Partitioning II | Solution | Solve | Hard | | |
| 135. Candy | Solution | Solve | Hard | | |
| 140. Word Break II | Solution | Solve | Hard | | |
| 149. Max Points on a Line | Solution | Solve | Hard | | |
| 154. Find Minimum in Rotated Sorted Array II | Solution | Solve | Hard | | |
| 174. Dungeon Game | Solution | Solve | Hard | | |
| 185. Department Top Three Salaries | Solution | Solve | Hard | | |
| 188. Best Time to Buy and Sell Stock IV | Solution | Solve | Hard | | |
| 212. Word Search II | Solution | Solve | Hard | | |
| 214. Shortest Palindrome | Solution | Solve | Hard | | |
| 218. The Skyline Problem | Solution | Solve | Hard | | |
| 220. Contains Duplicate III | Solution | Solve | Hard | | |
| 224. Basic Calculator | Solution | Solve | Hard | | |
| 233. Number of Digit One | Solution | Solve | Hard | | |
| 239. Sliding Window Maximum | Solution | Solve | Hard | | |
| 262. Trips and Users | Solution | Solve | Hard | | |
| 269. Alien Dictionary | Solution | Solve | Hard | | |
| 273. Integer to English Words | Solution | Solve | Hard | | |
| 295. Find Median from Data Stream | Solution | Solve | Hard | | |
| 296. Best Meeting Point | Solution | Solve | Hard | | |
| 297. Serialize and Deserialize Binary Tree | Solution | Solve | Hard | | |
| 301. Remove Invalid Parentheses | Solution | Solve | Hard | | |
| 312. Burst Balloons | Solution | Solve | Hard | | |
| 315. Count of Smaller Numbers After Self | Solution | Solve | Hard | | |
| 317. Shortest Distance from All Buildings | Solution | Solve | Hard | | |
| 321. Create Maximum Number | Solution | Solve | Hard | | |
| 329. Longest Increasing Path in a Matrix | Solution | Solve | Hard | | |
