| 125 | Valid Palindrome | Easy |
| 126 | Word Ladder II | Hard |
| 151 | Reverse Words in a String | Medium |
| 165 | Compare Version Numbers | Medium |
| 187 | Repeated DNA Sequences | Medium |
| 205 | Isomorphic Strings | Easy |
| 211 | Design Add and Search Words Data Structure | Medium |
| 214 | Shortest Palindrome | Hard |
| 224 | Basic Calculator | Hard |
| 227 | Basic Calculator II | Medium |
| 241 | Different Ways to Add Parentheses | Medium |
| 257 | Binary Tree Paths | Easy |
| 273 | Integer to English Words | Hard |
| 282 | Expression Add Operators | Hard |
| 290 | Word Pattern | Easy |
| 297 | Serialize and Deserialize Binary Tree | Hard |
| 299 | Bulls and Cows | Medium |
| 301 | Remove Invalid Parentheses | Hard |
| 306 | Additive Number | Medium |
| 318 | Maximum Product of Word Lengths | Medium |
| 331 | Verify Preorder Serialization of a Binary Tree | Medium |
| 336 | Palindrome Pairs | Hard |
| 344 | Reverse String | Easy |
| 345 | Reverse Vowels of a String | Easy |
| 385 | Mini Parser | Medium |
| 387 | First Unique Character in a String | Easy |
| 388 | Longest Absolute File Path | Medium |
| 389 | Find the Difference | Easy |
| 392 | Is Subsequence | Easy |
| 394 | Decode String | Medium |