Hash Table

Easy | Array, Hash Table, String

Medium | Array, Hash Table, Counting

Medium | Hash Table, Math

Medium | Hash Table, String, Bit Manipulation, Sliding Window

Medium | Array, Hash Table, Binary Search, Dynamic Programming

Hard | Array, Hash Table, Depth-First Search, Breadth-First Search

Medium | Array, Hash Table, Two Pointers, String, Dynamic Programming, Sorting

Medium | Array, Hash Table, Greedy, Sorting, Heap (Priority Queue), Counting

Medium | Array, Hash Table, Matrix

Hard | Array, Hash Table, Matrix, Prefix Sum