力扣-73.矩阵置零

题目描述

java 复制代码

class Solution {
    public void setZeroes(int[][] matrix) {
        int firstRow = 0;
        int firstCol = 0;
        int m = matrix.length;
        int n = matrix[0].length;
        for (int i = 0; i < n; i++) {
            if (matrix[0][i] == 0) {
                firstRow = 1;
            }
        }
        for (int i = 0; i < m; i++) {
            if (matrix[i][0] == 0) {
                firstCol = 1;
            }
        }
        for (int i = 1; i < m; i++) {
            for (int j = 1; j < n; j++) {
                if (matrix[i][j] == 0) {
                    matrix[0][j] = 0;
                    matrix[i][0] = 0;
                }
            }
        }
        for (int i = 1; i < n; i++) {
            if (matrix[0][i] == 0) {
                for (int j = 1; j < m; j++) {
                    matrix[j][i] = 0;
                }
            }
        }
        for (int i = 1; i < m; i++) {
            if (matrix[i][0] == 0) {
                for (int j = 1; j < n; j++) {
                    matrix[i][j] = 0;
                }
            }
        }
        if (firstRow == 1) {
            for (int i = 0; i < n; i++) {
                matrix[0][i] = 0;
            }
        }
        if (firstCol == 1) {
            for (int i = 0; i < m; i++) {
                matrix[i][0] = 0;
            }
        }
    }
}

小结：用两个额外变量来标记首行和首列是否有0，用首行和首列记录该行/列是否有0。