leetcode-Set Matrix Zeroes

Set Matrix Zeroes Total Accepted: 25064 Total Submissions: 80609 My Submissions Question Solution 
Given a m x n matrix, if an element is 0, set its entire row and column to 0. Do it in place.


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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?

class Solution {
public:
    void setZeroes(vector<vector<int> > &matrix) {
        
        int row1=1;
        int col1=1;

        int m=matrix.size();
        int n=matrix[0].size();

        //扫描第一行
        for(int j=0;j<n;j++)
            if(matrix[0][j]==0)
                row1=0;
        for(int i=0;i<m;i++)
            if(matrix[i][0]==0)
                col1=0;
        
                
        //扫描余下矩阵
        for(int i=1;i<m;i++)
        {
            for(int j=1;j<n;j++)
                if(matrix[i][j]==0)
                    matrix[i][0]=matrix[0][j]=0;
        }
        
        //行置0
        for(int i=1;i<m;i++)
            if(matrix[i][0]==0)
                for(int j=1;j<n;j++)
                    matrix[i][j]=0;
        
        //列置0
        for(int j=1;j<n;j++)
            if(matrix[0][j]==0)
                for(int i=1;i<m;i++)
                    matrix[i][j]=0;
                    
        //第一行置0
        if(row1==0)
        for(int j=0;j<n;j++)
            matrix[0][j]=0;
        
        //第一列置0
        if(col1==0)
        for(int i=0;i<m;i++)
            matrix[i][0]=0;
    }
};