73. Set Matrix Zeroes

Problem Statement

Medium

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.

Example 1:

Input: matrix = [[1,1,1],[1,0,1],[1,1,1]]
Output: [[1,0,1],[0,0,0],[1,0,1]]

Example 2:

Input: matrix = [[0,1,2,0],[3,4,5,2],[1,3,1,5]]
Output: [[0,0,0,0],[0,4,5,0],[0,3,1,0]]

Constraints:

m == matrix.length
n == matrix[0].length
1 <= m, n <= 200
-2³¹ <= matrix[i][j] <= 2³¹ - 1

Follow up:

A straightforward 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?

Java — hashsets of indices

Source file

class Solution {
    public void setZeroes(int[][] matrix) {
        int m = matrix.length, n = matrix[0].length;
        Set<Integer> Is = new HashSet<>();
        Set<Integer> Js = new HashSet<>();
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                if (matrix[i][j] == 0) {
                    Is.add(i);
                    Js.add(j);
                }
            }
        }
        for (int i = 0; i < m; i++)
            for (int j = 0; j < n; j++)
                if (Is.contains(i) || Js.contains(j))
                    matrix[i][j] = 0;
    }
}

Java

Source file

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