| 10 | Regular Expression Matching | Hard |
| 17 | Letter Combinations of a Phone Number | Medium |
| 22 | Generate Parentheses | Medium |
| 37 | Sudoku Solver | Hard |
| 39 | Combination Sum | Medium |
| 40 | Combination Sum II | Medium |
| 44 | Wildcard Matching | Hard |
| 46 | Permutations | Medium |
| 47 | Permutations II | Medium |
| 51 | N-Queens | Hard |
| 52 | N-Queens II | Hard |
| 60 | Permutation Sequence | Medium |
| 77 | Combinations | Medium |
| 78 | Subsets | Medium |
| 79 | Word Search | Medium |
| 89 | Gray Code | Medium |
| 90 | Subsets II | Medium |
| 93 | Restore IP Addresses | Medium |
| 126 | Word Ladder II | Hard |
| 131 | Palindrome Partitioning | Medium |
| 140 | Word Break II | Hard |
| 216 | Combination Sum III | Medium |
| 257 | Binary Tree Paths | Easy |
| 282 | Expression Add Operators | Hard |
| 301 | Remove Invalid Parentheses | Hard |
| 306 | Additive Number | Medium |
| 357 | Count Numbers with Unique Digits | Medium |
| 401 | Binary Watch | Easy |
| 473 | Matchsticks to Square | Medium |
| 491 | Increasing Subsequences | Medium |