Set Matrix Zeroes.txt

Given a m x n matrix, if an element is 0, set its entire row and column to 0. Do it in place.

click to show follow up.

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?

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思路：当检测到0时，把其所在行所在列元素置为标记数字，这里要注意所在行所在列还有其他0，应对其进行保留。
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class Solution {
public:
    void setFlag(vector<vector<int> > &matrix, int i, int j)
    {
        for(int p = 0; p < matrix[i].size(); p++)
            if(matrix[i][p] != 0)
                matrix[i][p] = -1;
        for(int p = 0; p < matrix.size(); p++)
            if(matrix[p][j] != 0)
                matrix[p][j] = -1;
    }

    void setZeroes(vector<vector<int> > &matrix) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        if(matrix.empty())
            return;
        for(int i = 0; i < matrix.size(); i++)
            for(int j = 0; j < matrix[0].size(); j++)
                if(matrix[i][j] == 0)
                {
                    matrix[i][j] = -1;
                    setFlag(matrix, i, j);
                }
        for(int i = 0; i < matrix.size(); i++)
            for(int j = 0; j < matrix[0].size(); j++)
            if(matrix[i][j] == -1)
                matrix[i][j] = 0;
    }
};