| 140 | Word Break II | Hard |
| 145 | Binary Tree Postorder Traversal | Hard |
| 146 | LRU Cache | Hard |
| 149 | Max Points on a Line | Hard |
| 154 | Find Minimum in Rotated Sorted Array II | Hard |
| 164 | Maximum Gap | Hard |
| 174 | Dungeon Game | Hard |
| 185 | Department Top Three Salaries | Hard |
| 188 | Best Time to Buy and Sell Stock IV | Hard |
| 212 | Word Search II | Hard |
| 214 | Shortest Palindrome | Hard |
| 218 | The Skyline Problem | Hard |
| 224 | Basic Calculator | Hard |
| 233 | Number of Digit One | Hard |
| 239 | Sliding Window Maximum | Hard |
| 262 | Trips and Users | Hard |
| 273 | Integer to English Words | Hard |
| 282 | Expression Add Operators | Hard |
| 295 | Find Median from Data Stream | Hard |
| 297 | Serialize and Deserialize Binary Tree | Hard |
| 301 | Remove Invalid Parentheses | Hard |
| 312 | Burst Balloons | Hard |
| 315 | Count of Smaller Numbers After Self | Hard |
| 316 | Remove Duplicate Letters | Hard |
| 321 | Create Maximum Number | Hard |
| 329 | Longest Increasing Path in a Matrix | Hard |
| 330 | Patching Array | Hard |
| 332 | Reconstruct Itinerary | Hard |
| 335 | Self Crossing | Hard |
| 336 | Palindrome Pairs | Hard |