Set Matrix Zeroes

Problem

Given an m x n integer matrix matrix, if an element is 0, set its entire row and column to 0's. You must do it in place.

Examples

The brute-force approach

Collect all (row, col) positions of zeros. Then zero out each such row and column.

zeros = [(r, c) for r in range(m) for c in range(n) if matrix[r][c] == 0]
for r, c in zeros:
    for j in range(n): matrix[r][j] = 0
    for i in range(m): matrix[i][c] = 0

O(m×n×(m+n)) — re-zeroing entire rows/columns for each zero. Or the naive approach that marks zeros during the same pass and confuses original vs. newly-added zeros.

Spotting the pattern

This is a Matrix Traversal problem. The key question to ask yourself:

Why do you need to record whether the first row and first column originally contained zeros before using them as markers? What goes wrong if you don't?

Answering that is where it clicks, and it's exactly what the guided walkthrough below builds with you: the pattern reasoning, a progressive hint ladder that never spoils the answer, a row-by-row dry run, the optimized solution, and an in-browser editor to run your code against real test cases.