Set Matrix Zeroes

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?

方法一：分别用两个向量标记哪一行和哪一列需要被置为0，需要O(m+n)额外空间

方法二：使用matrix的第一行和第一列标记该列/行是否需要被置为0，matrix[0][0]需要额外设置一个bool变量标记列，需要一个bool的额外空间。

这样的话需要注意清零的顺序，代码如下：

class Solution {public:    void setZeroes(vector<vector<int> > &matrix) {        // Start typing your C/C++ solution below        // DO NOT write int main() function                        int n = matrix.size();        int m = matrix[0].size();        if(m < 1 && n < 1) return;                bool first_column_clear = false;                for(int i = 0; i < n;i++)        {            if(matrix[i][0] == 0){                first_column_clear = true;                break;            }        }                for(int i = 0; i < n;i++)        {            for(int j = 1; j < m;j++)            {                if(matrix[i][j] == 0){                    matrix[0][j] = 0;                    matrix[i][0] = 0;                }            }        }                for(int j = 1;j < m;j++)        {            if(matrix[0][j] == 0){                for(int i = 1;i < n;i++)                    matrix[i][j] = 0;            }        }                for(int i = 0;i < n;i++)        {           if(matrix[i][0] == 0){               for(int j = 1;j < m;j++)                    matrix[i][j] = 0;           }        }                               if(first_column_clear){            for(int i = 0;i<n;i++)            {                matrix[i][0] = 0;            }        }            }};

356 milli secs.