Essential 75

Foundation problems covering hash maps, two pointers, sliding window, and binary search on arrays.

Bit manipulation techniques including XOR tricks, bit counting, and bitwise arithmetic.

Classic DP patterns: climbing stairs, knapsack variants, sequence problems, and grid traversal.

Graph traversal, cycle detection, topological sort, union-find, and connected components.

Interval merging, insertion, scheduling, and overlap detection problems.

Pointer manipulation, reversal, cycle detection, merging, and two-pointer techniques on linked lists.

2D array traversal patterns including spiral order, rotation, and backtracking search.

Sliding window, two pointers, anagram detection, palindromes, and encoding problems.

Binary tree traversal, BST properties, serialization, tries, and recursive tree algorithms.

Priority queue problems including top-k elements and streaming median.