Blog

Grid navigation, sequence alignment, and string transformation — three canonical 2D DSA DP patterns explained with JavaScript, tables, and interview-ready solutions.

DP doesn't have to be scary. Learn the framework — define state, write recurrence, nail base cases — through Climbing Stairs, House Robber, and Coin Change.

Grid problems are graph problems in disguise. Learn the DFS/BFS traversal pattern that unlocks Number of Islands, Clone Graph, and Pacific Atlantic Water Flow.

Topological sort is how you order things with dependencies. Learn the DFS three-state and Kahn's BFS approaches to ace Course Schedule, Course Schedule II, and Alien Dictionary.

Multi-source BFS is single-source BFS with all starting points seeded at once. Master this pattern and you can solve Rotting Oranges, Walls and Gates, and Word Ladder in one mental model.

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.