Array

Hard | Array, Bit Manipulation, Tree, Depth-First Search

Medium | Array, Linked List, Matrix, Simulation

Hard | Array, Dynamic Programming, Depth-First Search, Breadth-First Search, Graph Theory, Topological Sort, Memoization, Matrix

Medium | Array, Two Pointers, Binary Search, Sorting

Hard | Array, Stack, Union-Find, Monotonic Stack

Easy | Array, Greedy, Sorting, Heap (Priority Queue)

Easy | Array, Hash Table, Counting

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

Medium | Array, String, Divide and Conquer, Sorting, Heap (Priority Queue), Radix Sort, Quickselect

Hard | Array, Math, Sorting, Heap (Priority Queue), Number Theory