Array

Hard | Array, Binary Search, Greedy, Sorting, Prefix Sum

Hard | Array, Greedy, Sorting

Easy | Array, Hash Table, String

Medium | Array, String, Trie

Medium | Array, Hash Table, Counting

Hard | Array, Binary Search, Stack, Sorting, Heap (Priority Queue), Monotonic Stack

Easy | Array, Math

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

Hard | Array, Tree, Depth-First Search, Breadth-First Search, Binary Tree

Easy | Array, Two Pointers, Simulation