Algorithm questions daily practice---Day 79: Matrix zeroing

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1. Problem description

Given a  m x n matrix, if an element is  0 , set all elements in its row and column to  0  . Please use an in  -place algorithm.

Topic link: Matrix zeroing

Second, the subject requirements

Example 1

输入： matrix = [[1,1,1],[1,0,1],[1,1,1]]
输出： [[1,0,1],[0,0,0],[1,0,1]]
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Example 2

输入： matrix = [[0,1,2,0],[3,4,5,2],[1,3,1,5]]
输出： [[0,0,0,0],[0,4,5,0],[0,3,1,0]]
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visit

1.数组
2.建议用时15~25min
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3. Problem Analysis

This is a question that examines the logic of array thinking. For a given array at the beginning, a loop judgment is performed first.

If the position contains 0, then to record this position, what record is used?

We can construct the two arrays separately

vector<int>row(m),col(n);//行、列数组
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Store 0 position, the data of this entire row and column.

Finally, traverse the row and column where the current element is located. If it is found row[i]或者col[j]to be equal to 1, then set the element to 0.

Fourth, the encoding implementation

class Solution {
public:
    void setZeroes(vector<vector<int>>& matrix) {
        int i,j,p=0,m=matrix.size(),n=matrix[0].size();//初始化数据
        vector<int>row(m),col(n);//行、列数组
        for(i=0;i<m;i++)//遍历求解位置
        {
            for(j=0;j<n;j++)
            {
                if(matrix[i][j]==0)
                {
                    row[i]=col[j]=1;//暂存行、列
                }
            }
        }
        for(i=0;i<m;i++)//之前记录位置的行、列置为0
        {
            for(j=0;j<n;j++)
            {
                if(row[i]||col[j])
                {
                    matrix[i][j]=0;
                }
            }
        }
    }
};

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5. Test results