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]
]




思路：
用矩阵的第一行存储，哪一列需要置0
用矩阵的第一列存储，哪一行需要置0

class Solution {
public:
    void setZeroes(vector<vector<int>>& matrix) {
        int rows = matrix.size();
        int cols = matrix[0].size();
        int col0=1,row0=1;

        
        for(int i = 0;i<rows;i++)
            if(matrix[i][0]==0)col0=0;
        
        for(int j = 0;j<cols;j++)
            if(matrix[0][j]==0)row0=0;
        
        
        
        for(int i = 1;i<rows;i++)
            for(int j = 1;j<cols;j++)
                if(matrix[i][j]==0){
                    matrix[0][j] = 0;
                    matrix[i][0] = 0;
                }
    
        
        
        for(int i = 1;i<rows;i++)
              for(int j = 1;j<cols;j++)
                if(matrix[i][0]==0||matrix[0][j]==0)
                    matrix[i][j]=0;
        
        if(col0==0){
            for(int i = 0;i<rows;i++)
                matrix[i][0] = 0;
        }
        if(row0==0){
        for(int j = 0;j<cols;j++)
            matrix[0][j]= 0 ;
        }
        
    }
};