Sorted arrays, pairs, in-place ops

Subarrays, substrings, fixed/variable window

LIFO, parentheses, monotonic stack

O(log n) search, search space reduction

Pointers, reversal, cycle detection

DFS, BFS, BST properties

Top K, median, scheduling

Combinations, permutations, constraint satisfaction

DFS, BFS, topological sort, shortest path

Memoization, tabulation, optimal substructure

Merge, insert, overlap detection

Local optimal → global optimal

2D traversal, rotation, spiral