LeetCode 之 Set Matrix Zeroes

原题：

Given a m x n matrix, if an element is 0, set its entire row and column to 0. Do it in place.

click to show follow up.

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?

我用的就是O（m+n），即遍历数组，用row和col来保存要设为0的行和列，用的是unordered_set。。。有时间再优化。。。。。先睡了

代码如下（284ms）：

class Solution {public:    void setZeroes(vector<vector<int> > &matrix) {                unordered_set<int> row;        unordered_set<int> col;                for (int i=0;i<matrix.size();i++){            for(int j=0;j<matrix[i].size();j++){                if(matrix[i][j] == 0){                    if(row.find(i) == row.end()) row.insert(i);                    if(col.find(j) == col.end()) col.insert(j);                }             }        }                for ( auto it = row.begin(); it != row.end(); ++it )        {            for(int i =0 ;i<matrix[*it].size();i++){                matrix[*it][i] = 0;            }        }                            for ( auto it = col.begin(); it != col.end(); ++it )        {            for(int i =0 ;i<matrix.size();i++){                matrix[i][*it] = 0;            }        }    }};