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.