19.2.13 [LeetCode 73] 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.

Example 1:

Input: 
[
  [1,1,1],
  [1,0,1],
  [1,1,1]
]
Output: 
[
  [1,0,1],
  [0,0,0],
  [1,0,1]
]

Example 2:

Input: 
[
  [0,1,2,0],
  [3,4,5,2],
  [1,3,1,5]
]
Output: 
[
  [0,0,0,0],
  [0,4,5,0],
  [0,3,1,0]
]

Follow up:

• 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?

题意

矩阵中把所有包含0的行和列全部归0

题解

class Solution {
public:
    void setZeroes(vector<vector<int>>& matrix) {
        int m = matrix.size(), n = matrix[0].size();
        bool row = false, colum = false;
        for (int i = 0; i < m; i++)
            for (int j = 0; j < n; j++) {
                if (matrix[i][j] == 0) {
                    if (i == 0)row = true;
                    if (j == 0)colum = true;
                    if(i!=0)
                        matrix[i][0] = 0;
                    if(j!=0)
                        matrix[0][j] = 0;
                }
            }
        for (int i = 1; i < m; i++)
            for (int j = 1; j < n; j++)
                if (!matrix[i][0] || !matrix[0][j])
                    matrix[i][j] = 0;
        if (colum) {
            for (int i = 0; i < m; i++)
                matrix[i][0] = 0;
        }
        if(row){
            for (int j = 0; j < n; j++)
                matrix[0][j] = 0;
        }
    }
};

我一开始都没get到点在哪，试错之后才发现难点在哪……稍微用俩bool对 matrix[0][0] 的特殊情况处理一下就可以了