Recursion
50 problems — 5 easy, 29 medium, 16 hard.
| # | Title | Difficulty | Frequency |
|---|---|---|---|
| 10 | Regular Expression Matching | hard | company favorite |
| 17 | Letter Combinations of a Phone Number | medium | frequently asked |
| 37 | Sudoku Solver | hard | classic |
| 38 | Count and Say | medium | frequently asked |
| 39 | Combination Sum | medium | frequently asked |
| 40 | Combination Sum II | medium | frequently asked |
| 44 | Wildcard Matching | hard | company favorite |
| 46 | Permutations | medium | foundational |
| 47 | Permutations II | medium | frequently asked |
| 51 | N-Queens | hard | classic |
| 52 | N-Queens II | hard | classic |
| 60 | Permutation Sequence | hard | frequently asked |
| 77 | Combinations | medium | foundational |
| 78 | Subsets | medium | foundational |
| 79 | Word Search | medium | frequently asked |
| 87 | Scramble String | hard | less common |
| 89 | Gray Code | medium | less common |
| 90 | Subsets II | medium | frequently asked |
| 93 | Restore IP Addresses | medium | frequently asked |
| 97 | Interleaving String | medium | frequently asked |
| 113 | Path Sum II | medium | frequently asked |
| 115 | Distinct Subsequences | hard | frequently asked |
| 131 | Palindrome Partitioning | medium | frequently asked |
| 140 | Word Break II | hard | frequently asked |
| 172 | Factorial Trailing Zeroes | medium | frequently asked |
| 212 | Word Search II | hard | frequently asked |
| 216 | Combination Sum III | medium | frequently asked |
| 247 | Strobogrammatic Number II | medium | less common |
| 257 | Binary Tree Paths | easy | foundational |
| 273 | Integer to English Words | hard | company favorite |
| 282 | Expression Add Operators | hard | company favorite |
| 326 | Power of Three | easy | foundational |
| 377 | Combination Sum IV | medium | frequently asked |
| 386 | Lexicographical Numbers | medium | less common |
| 401 | Binary Watch | easy | less common |
| 404 | Sum of Left Leaves | easy | foundational |
| 416 | Partition Equal Subset Sum | medium | frequently asked |
| 446 | Arithmetic Slices II - Subsequence | hard | less common |
| 488 | Zuma Game | hard | less common |
| 509 | Fibonacci Number | easy | foundational |
| 526 | Beautiful Arrangement | medium | less common |
| 638 | Shopping Offers | medium | less common |
| 639 | Decode Ways II | hard | company favorite |
| 784 | Letter Case Permutation | medium | frequently asked |
| 797 | All Paths From Source to Target | medium | frequently asked |
| 894 | All Possible Full Binary Trees | medium | less common |
| 967 | Numbers With Same Consecutive Differences | medium | less common |
| 980 | Unique Paths III | hard | less common |
| 1079 | Letter Tile Possibilities | medium | frequently asked |
| 1239 | Maximum Length of a Concatenated String with Unique Characters | medium | frequently asked |