| Longest Common Prefix |
O(S) where S = sum of all string lengths |
Autocomplete, trie-based search, file path commonality. Simple but |
| Longest Palindromic Substring |
O(n²) |
Substring search with symmetry constraint. Related to Manacher's |
| String To Integer Atoi |
O(n) |
Parsing problems, state machine patterns. Tests attention to edge |
| Valid Anagram |
O(n) with Counter, O(n log n) with sort |
Equivalence class membership — same chars different order. Group |
| Valid Palindrome |
O(n) |
String validity checks, symmetry problems. Foundation for palindrome |