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?

 

Code:

 

?

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

class Solution { public:     void setZeroes(vector<vector<int> > &matrix) {         int m=matrix.size();         int n=matrix[0].size();         int firstrow=0;         int firstcol=0;         for(int i=0;i<n;i++)             if(matrix[0][i]==0){                 firstrow=1;                 break;             }         for(int j=0;j<m;j++)             if(matrix[j][0]==0){                 firstcol=1;                 break;             }         for(int j=0;j<m;j++)             for(int i=0;i<n;i++){                 if(matrix[j][i]==0){                     matrix[j][0]=0;                     matrix[0][i]=0;                 }             }         for(int i=1;i<n;i++)             if(matrix[0][i]==0)                 for(int j=1;j<m;j++)                     matrix[j][i]=0;         for(int j=1;j<m;j++)             if(matrix[j][0]==0)                 for(int i=1;i<n;i++)                     matrix[j][i]=0;         if(firstrow==1)             for(int i=0;i<n;i++)                     matrix[0][i]=0;         if(firstcol==1)             for(int j=1;j<m;j++)                     matrix[j][0]=0;     } };