[LeetCode] 73. Set Matrix Zeroes 解题思路

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?

问题：给定一个矩阵，当矩阵一个元素为 0 ，将该元素的当前行，当前列都设为 0 。

我的方案满足补充内容的第二点，使用 O(m + n) 额外空间。

• 将矩阵中所有 0 元素的所在行，列记录下来。
• 将记录下来的行号，整行设为0，将记录下来的列号，整列设为0.

 void setZeroes(vector<vector<int>>& matrix) {

     unordered_set<int> seti;
     unordered_set<int> setk;

     for (int i =  ; i < matrix.size(); i++) {
         for (int k =  ; k < matrix[].size(); k++) {
             if (matrix[i][k] == ) {
                 seti.insert(i);
                 setk.insert(k);
             }
         }
     }

     unordered_set<int>::iterator s_iter;
     for (s_iter = seti.begin(); s_iter != seti.end(); s_iter++) {
         for (int k =  ; k < matrix[].size(); k++) {
             matrix[*s_iter][k] = ;
         }
     }

     for (s_iter = setk.begin(); s_iter != setk.end(); s_iter++) {
         for (int i = ; i < matrix.size(); i++) {
             matrix[i][*s_iter] = ;
         }
     }
 }