README.md

Set Matrix Zeroes

Solution 1

/**
 * Question   : 73. Set Matrix Zeroes
 * Complexity : Time: O(m*n) ; Space: O(m+n)
 * Topics     : Array, Matrix
 */
class Solution {
    public void setZeroes(int[][] matrix) {
        int m = matrix.length;
        int n = matrix[0].length;

        boolean[] rowZero = new boolean[m];
        boolean[] colZero = new boolean[n];

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

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

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

Solution 2

/**
 * Question   : 73. Set Matrix Zeroes
 * Topics     : Matrix
 * Complexity : Time: O(m*n) ; Space: O(1)
 */
class Solution {
    public void setZeroes(int[][] matrix) {
        // We use first row and first col as marker.
        boolean firstRowZero = false;
        boolean firstColZero = false;

        for (int j = 0; j < matrix[0].length; j++) {
            if (matrix[0][j] == 0) {
                firstRowZero = true;
                break;
            }
        }
        for (int i = 0; i < matrix.length; i++) {
            if (matrix[i][0] == 0) {
                firstColZero = true;
                break;
            }
        }

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

        for (int i = 1; i < matrix.length; i++) {
            for (int j = 1; j < matrix[0].length; j++) {
                if (matrix[0][j] == 0 || matrix[i][0] == 0) {
                    matrix[i][j] = 0;
                }
            }
        }

        if (firstRowZero) {
            for (int j = 0; j < matrix[0].length; j++) {
                matrix[0][j] = 0;
            }
        }
        if (firstColZero) {
            for (int i = 0; i < matrix.length; i++) {
                matrix[i][0] = 0;
            }
        }
    }
}