题目

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

click to show follow up.

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?

解析

class Solution {
    public void setZeroes(int[][] matrix) {
        //判断一列是否为0
        int col = 1;
        int rows = matrix.length;
        int cols = matrix[0].length;
        for (int i = 0; i < rows; i++) {
            if (matrix[i][0] == 0) col = 0;
            for (int j = 1; j < cols; j++) {
                if (matrix[i][j] == 0) {
                    matrix[i][0] = 0;
                    matrix[0][j] = 0;
                }
            }
        }
        for (int i = rows - 1; i >= 0; i--) {
            for (int j = cols - 1; j >= 1; j--) {
                if (matrix[i][0] == 0 || matrix[0][j] == 0) {
                    matrix[i][j] = 0;
                }
            }
            if (col == 0) {
                matrix[i][0] = 0;
            }
        }
    }
}