| 1. Two Sum | brute force, two-pass hash table, one-pass hash table |
| 14. Longest Common Prefix | brute force - horizontal, brute force - vertical |
| 169. Majority Element | one-pass or two-pass hash table, boyer-moore voting algorithm |
| 217. Contains Duplicate | brute force, sorting, one-pass hash table |
| 242. Valid Anagram | sorting, hash table |
| 303. Range Sum Query - Immutable | brute force, prefix sum |
| 383. Ransom Note | hash table (1 dict count), hash table (2 dict counts) |
| 409. Longest Palindrome | one-pass hash table - logic |
| 448. Find All Numbers Disappeared in an Array | two-pass with index marking |
| 705. Design HashSet | x |
| 706. Design HashMap | x |