073_SetMatrixZeroes73.java

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

public class SetMatrixZeroes73 {
    public void setZeroes(int[][] matrix) {
        boolean[] rows = new boolean[matrix.length];
        boolean[] cols = new boolean[matrix[0].length];

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

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

    }

    /**
     * https://leetcode.com/problems/set-matrix-zeroes/discuss/26008/My-AC-java-O(1)-solution-(easy-to-read)
     */
    public void setZeroes2(int[][] matrix) {
        boolean fr = false,fc = false;
        for(int i = 0; i < matrix.length; i++) {
            for(int j = 0; j < matrix[0].length; j++) {
                if(matrix[i][j] == 0) {
                    if(i == 0) fr = true;
                    if(j == 0) fc = true;
                    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[i][0] == 0 || matrix[0][j] == 0) {
                    matrix[i][j] = 0;
                }
            }
        }
        if(fr) {
            for(int j = 0; j < matrix[0].length; j++) {
                matrix[0][j] = 0;
            }
        }
        if(fc) {
            for(int i = 0; i < matrix.length; i++) {
                matrix[i][0] = 0;
            }
        }

    }

}