Problem #73: Set Matrix Zeroes

Intuition & Strategy Breakdown

Use first row and first column as marker flags to track zero rows/columns. Use two separate boolean variables for whether row 0 and col 0 initially contain zeros.

Python Solution

def setZeroes(matrix):
    m, n = len(matrix), len(matrix[0])
    row0 = any(matrix[0][j] == 0 for j in range(n))
    col0 = any(matrix[i][0] == 0 for i in range(m))
    
    for i in range(1, m):
        for j in range(1, n):
            if matrix[i][j] == 0:
                matrix[i][0] = matrix[0][j] = 0
                
    for i in range(1, m):
        for j in range(1, n):
            if matrix[i][0] == 0 or matrix[0][j] == 0:
                matrix[i][j] = 0
                
    if row0:
        for j in range(n): matrix[0][j] = 0
    if col0:
        for i in range(m): matrix[i][0] = 0

Java Solution

class Solution {
    public void setZeroes(int[][] matrix) {
        int m = matrix.length, n = matrix[0].length;
        boolean row0 = false, col0 = false;
        
        for (int j = 0; j < n; j++) if (matrix[0][j] == 0) row0 = true;
        for (int i = 0; i < m; i++) if (matrix[i][0] == 0) col0 = true;
        
        for (int i = 1; i < m; i++) {
            for (int j = 1; j < n; j++) {
                if (matrix[i][j] == 0) {
                    matrix[i][0] = 0;
                    matrix[0][j] = 0;
                }
            }
        }
        
        for (int i = 1; i < m; i++) {
            for (int j = 1; j < n; j++) {
                if (matrix[i][0] == 0 || matrix[0][j] == 0) {
                    matrix[i][j] = 0;
                }
            }
        }
        
        if (row0) for (int j = 0; j < n; j++) matrix[0][j] = 0;
        if (col0) for (int i = 0; i < m; i++) matrix[i][0] = 0;
    }
}