Set Matrix Zeroes (LeetCode)

Question:

https://oj.leetcode.com/problems/set-matrix-zeroes/

 

解答：

可以用external space的话，可以用两个array, A[N] and B[M]. 当matrix[i][j] == 0，就把A[i]和B[j]设成0，最后matrix[i][j] = 0 if A[i]==0 || B[j] == 0

如果不能用外部空间，可以用第一行和第一列来做类似的工作。只是需要事先记录下第一行和第一列本身有没有0.

 

class Solution {
public:
    void setZeroes(vector<vector<int> > &matrix) {
        
        int row = matrix.size();
        if (row == 0)
            return;
            
        int col = matrix[0].size();
        if (col == 0)
            return;
            
        // handle the first row/col
        bool firstRow = false;
        bool firstCol = false;
        
        for (int i = 0; i < row; i++)
        {
            if (matrix[i][0] == 0)
            {
                firstCol = true;
                break;
            }
        }
        
        for (int i = 0; i < col; i++)
        {
            if (matrix[0][i] == 0)
            {
                firstRow = true;
                break;
            }
        }

        for (int i = 1; i < row; i++)
        {
            for (int j = 1; j < col; j++)
            {
                if (matrix[i][j] == 0)
                {
                    matrix[0][j] = 0;
                    matrix[i][0] = 0;
                }
            }
        }
        
        for (int i = 1; i < row; i++)
        {
            for (int j = 1; j < col; j++)
            {
                if (matrix[0][j] == 0 || matrix[i][0] == 0)
                    matrix[i][j] = 0;
            }
        }
        
        if (firstCol)
        {
            for (int i = 0; i < row; i++)
                matrix[i][0] = 0;
        }
        
        if (firstRow)
        {    
            for (int i = 0; i < col; i++)
                matrix[0][i] = 0;
        }
    }
};