73. Set Matrix Zeroes

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?

Solution:

class Solution {
    public void setZeroes(int[][] matrix) {
        int row = matrix.length;
        int col = matrix[0].length;
        Set<Integer> rows = new HashSet<Integer>();
        Set<Integer> cols = new HashSet<Integer>();

        for (int i = 0; i < row; i++){
            for (int j = 0; j < col; j++){
                if (matrix[i][j] == 0){
                    rows.add(i);
                    cols.add(j);
                }
            }
        }

        for (int i = 0; i < row; i++){
            for (int j = 0; j < col; j++){
                if (rows.contains(i) || cols.contains(j)){
                    matrix[i][j] = 0;
                }
            }
        }

    }
}

// TC:O(m*n)
// SC:O(m+n)