73. Set Matrix Zeroes

Set Matrix Zeroes

Given a m x n matrix, if an element is 0, set its entire row and column to 0. Do it in place.

click to show follow up.

Follow up:

Did you use extra space? A straight forward solution using O(mn) space is probably a bad idea. A simple improvement uses O(m + n) space, but still not the best solution. Could you devise a constant space solution?

Solution

public class Solution {
    public void setZeroes(int[][] matrix) {
        int m = matrix.length;
        int n = matrix[0].length;

        boolean firstRow = false;
        boolean firstColumn = false;

        for(int i = 0; i <m; i ++) {
            if (matrix[i][0] == 0) {
                firstColumn = true;
            }
        }

        for(int i = 0; i < n; i ++) {
            if (matrix[0][i] == 0) {
                firstRow = 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 ++) {
            if (matrix[i][0] == 0) {
                for(int j = 0; j < n; j ++) {
                    matrix[i][j] = 0;
                }
            }
        }

        for(int i = 1; i < n; i ++) {
            if (matrix[0][i] == 0) {
                for(int j = 0; j < m; j ++) {
                    matrix[j][i] = 0;
                }
            }
        }

        if (firstColumn) {
            for(int i = 0; i < m; i ++) {
                matrix[i][0] = 0;
            }
        }

        if (firstRow) {
            for(int j = 0; j < n; j ++) {
                matrix[0][j] = 0;
            }
        }
    }
}