Array

Medium | Array, Hash Table

Hard | Array, Hash Table, Tree, Graph Theory, Simulation

Medium | Array, Greedy, Sorting, Matrix

Medium | Array, Breadth-First Search, Matrix

Hard | Array, Dynamic Programming

Medium | Array, Dynamic Programming, Backtracking

Hard | Array, Math, Stack, Heap (Priority Queue), Monotonic Stack

Hard | Array, Hash Table, Dynamic Programming, Bit Manipulation, Counting

Medium | Array, Greedy, Heap (Priority Queue)

Hard | Array, Bit Manipulation, Trie