$ ls patterns/

The bread and butter — arrays, strings, hashmaps, frequency counting, prefix sums.

Opposing or same-direction pointers turn O(n²) pair-search into O(n).

Expand-shrink template for longest/shortest substring or subarray with property.

LIFO + monotonic stack — next greater/smaller, parsing, histogram problems.

Halve search space. Master one template — including search-on-answer.

Dummy head, fast/slow pointers, reversal, in-place rearrangement, LRU.

Recursion + traversals. BST, BFS, postorder reductions, local+global tracking.

Prefix tree for autocomplete, dictionary, word-search-on-grid problems.

Top K, two heaps for medians, k-way merge, scheduling.

Recursion with undo. Subsets, permutations, combinations, N-Queens.

BFS, DFS, islands, topological sort, cycle detection.

Dijkstra, Bellman-Ford, Union-Find, MST.

Fibonacci-style, House Robber, Coin Change, LIS, Word Break.

Grid DP, knapsack, LCS, edit distance, interval DP.

Local-optimal proofs, jump game, interval scheduling/merging.

XOR tricks, bitmask DP, popcount, common idioms.