set-matrix-zeroes

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(m n) 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?

程序：

class Solution {public:    void setZeroes(vector<vector<int> > &matrix) {        const int row = matrix.size();        const int col = matrix[0].size();        bool row_flg = false, col_flg = false;                 //判断第一行和第一列是否有零，防止被覆盖        for (int i = 0; i < row; i++)            if (0 == matrix[i][0]) {                col_flg = true;                break;            }        for (int i = 0; i < col; i++)            if (0 == matrix[0][i]) {                row_flg = true;                break;            }        //遍历矩阵，用第一行和第一列记录0的位置        for (int i = 1; i < row; i++)            for (int j = 1; j < col; j++)                if (0 == matrix[i][j]) {                    matrix[i][0] = 0;                    matrix[0][j] = 0;                }        //根据记录清零        for (int i = 1; i < row; i++)            for (int j = 1; j < col; j++)                if (0 == matrix[i][0] || 0 == matrix[0][j])                    matrix[i][j] = 0;        //最后处理第一行        if (row_flg)            for (int i = 0; i < col; i++)                matrix[0][i] = 0;        if (col_flg)            for (int i = 0; i < row; i++)                matrix[i][0] = 0;    }};