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

O(mn) time O(m + n) space two pass solution

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public class Solution {
    public void setZeroes(int[][] matrix) {
        HashSet<Integer> rows = new HashSet<>();
        HashSet<Integer> cols = new HashSet<>();
        for (int i = 0; i < matrix.length; i++) {
            for (int j = 0; j < matrix[0].length; j++) {
                if (matrix[i][j] == 0) {
                    rows.add(i);
                    cols.add(j);
                }
            }
        }
        
        for (int row : rows) {
            for (int i = 0; i < matrix[0].length; i++) {
                if (matrix[row][i] != 0) {
                    matrix[row][i] = 0;
                }
            }
        }
        
        for (int col : cols) {
            for (int i = 0; i < matrix.length; i++) {
                if (matrix[i][col] != 0) {
                    matrix[i][col] = 0;
                }
            }
        }
    }
}

O(mn) time O(1) space two pass solution

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public class Solution {
    public void setZeroes(int[][] matrix) {
        int col0 = 1;
        for (int i = 0; i < matrix.length; i++) {
            if (matrix[i][0] == 0) {
                col0 = 0;
            }
            for (int j = 1; j < matrix[0].length; j++) {
                if (matrix[i][j] == 0) {
                    matrix[i][0] = 0;
                    matrix[0][j] = 0;
                }
            }
        }
        
        // start from right bottom corner
        // if start from left upper corner, must start from (1,1)
        // the first column should be set only after setting 
        // the rest matrix
        for (int i = matrix.length - 1; i >= 0; i--) {
            for (int j = matrix[0].length - 1; j >= 1; j--) {
                if (matrix[i][0] == 0 || matrix[0][j] == 0) {
                    matrix[i][j] = 0;
                }
            }
            if (col0 == 0) {
                matrix[i][0] = 0;
            }
        }
    }
}