8 articles
Traverse an m×n matrix in spiral order. Master the boundary-shrinking technique — maintain top, bottom, left, right walls and peel layer by layer. Covers edge cases, visual dry run, common bugs, Python & JavaScript solutions, and follow-ups like Spiral Matrix II.
Learn how to rotate an n×n matrix 90° clockwise in-place using the elegant transpose-then-reverse trick. Understand the math behind it, see the 4-cell direct rotation alternative, dry-run through a worked example, avoid the four most common mistakes, and get clean Python + JavaScript solutions.
Find the kth smallest element in a row-column sorted matrix by binary searching on the value range.
Count (row, col) pairs that are equal by hashing each row tuple and each column tuple.
Find the maximal rectangle in a binary matrix by building histogram heights row by row and applying largest rectangle.
Solve linear recurrences like Fibonacci in O(log n) using matrix exponentiation. Essential for DP optimization on large n.
Search for a target in a matrix where each row and column is sorted. O(m+n) solution using top-right corner elimination — a classic Google interview problem.
Calculate how much water can be trapped in a 3D height matrix. Uses a min-heap BFS starting from the boundary, always processing the lowest border cell to determine water trapped inside.