Blog

Backtracking is just DFS with an undo step. Master the three templates for subsets, permutations, and combinations — and the one mistake that ruins every solution.

N-Queens separates candidates who know backtracking from those who understand constraint propagation. The O(1) diagonal check using sets is what interviewers want to see.

The duplicate-skip pattern is what separates Combination Sum I from II. Master sort + skip, in-place grid marking for Word Search, and why `i > start` matters.

BST problems aren't just binary tree problems — the sorted-order property changes everything. Master validate, kth smallest, and the iterator pattern that shows up in real interviews.

Three linked list problems, one underlying playbook: dummy heads, divide-and-conquer merging, and the find-middle/reverse/interleave pipeline that makes LC 143 tractable.

One BFS template, three interview problems. Level-order, zigzag traversal, and right side view all reduce to the same queue loop with a small variation each time.

Post-order DFS, the global-state side-effect trick, and nested tree matching — four problems that teach you everything about recursive tree traversal in JavaScript.

The three-pointer pattern is the foundation of every linked list reversal. Understand it once and LC 206, 92, and 25 become variations on the same idea.

Two matrix search problems, two completely different optimal approaches. Learn when to use virtual 1D binary search vs the staircase elimination — the distinction that trips up most candidates.