| 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 |
| 224 | Basic Calculator | Hard |
| 290 | Word Pattern | Easy |
| 383 | Ransom Note | Easy |
| 387 | First Unique Character in a String | Easy |
| 389 | Find the Difference | Easy |
| 392 | Is Subsequence | Easy |
| 459 | Repeated Substring Pattern | Easy |
| 514 | Freedom Trail | Hard |
| 516 | Longest Palindromic Subsequence | Medium |
| 537 | Complex Number Multiplication | Medium |
| 556 | Next Greater Element III | Medium |
| 557 | Reverse Words in a String III | Easy |
| 606 | Construct String from Binary Tree | Easy |
| 649 | Dota2 Senate | Medium |
| 712 | Minimum ASCII Delete Sum for Two Strings | Medium |
| 752 | Open the Lock | Medium |
| 844 | Backspace String Compare | Easy |
| 859 | Buddy Strings | Easy |
| 862 | Find And Replace in String | Medium |
| 880 | Decoded String at Index | Medium |
| 984 | String Without AAA or BBB | Medium |
| 1047 | Remove All Adjacent Duplicates In String | Easy |
| 1048 | Longest String Chain | Medium |
| 1092 | Shortest Common Supersequence | Hard |