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?

思路

直接的思路是用o（m+n）的空间来记录m行和n列是否存在0， 但是需要用固定空间的解决方法，可以考虑使用原先数据提供的空间，进而想到用原数组的第一行和第一列来记录。另外由于还需要第一行和第一列是否需要置为0，所以使用两个bool变量来存储原先第一行和第一列是否存在0即可。

代码

    void setZeroes(vector<vector<int> > &matrix) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        bool hasZeroRow = false, hasZeroColumn = false;
        int i,j;
        int m = matrix.size();
        if(m == 0)
            return;
        int n = matrix[0].size();
        if(n == 0)
            return;
        for(i = 0; i < n; i++){
            if(matrix[0][i] == 0){
                hasZeroRow = true;
                break;
            }
        }
        for(i = 0; i < m; i++){
            if(matrix[i][0] == 0){
                hasZeroColumn = true;
                break;
            }
        }
        for(i = 1; i < m; i++){
            for(j = 1; j < n; j++){
                if(matrix[i][j] == 0){
                    matrix[0][j] = 0;
                    matrix[i][0] = 0;
                }
            }
        }
        for(i = 1; i < n; i++){
            if(matrix[0][i] == 0){
                for(j = 0; j < m; j++){
                    matrix[j][i] = 0;
                }
            }
        }
        for(i = 1; i < m; i++){
            if(matrix[i][0] == 0){
                for(j = 0; j < n; j++){
                    matrix[i][j] = 0;
                }
            }
        }
        if(hasZeroRow){
            for(i = 0; i < n; i++)
                matrix[0][i] = 0;
        }
        if(hasZeroColumn){
            for(i = 0; i < m; i++)
                matrix[i][0] = 0;
        }
    }