Array

Medium | Array, Hash Table, Simulation

Hard | Array, Math, Greedy

Easy | Array, Hash Table, Two Pointers, Enumeration

Medium | Array, Hash Table, Tree, Depth-First Search, Breadth-First Search, Union-Find, Graph Theory

Medium | Array, Dynamic Programming

Easy | Array, Matrix

Medium | Array, String, Prefix Sum

Hard | Array, Union-Find, Prefix Sum, Ordered Set

Easy | Array, Greedy

Hard | Array, Sorting, Heap (Priority Queue)