LeetCodeのSet Matrix Zeroes

原題:
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?
私が使っているのはO(m+n)、つまり配列を遍歴し、rowとcolで0に設定する行と列を保存し、unordered_を使っています.set...また最適化する時間があります....先に寝て
コードは以下の通り(284 ms):

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;
            }
        }
    }
};