[LeetCode]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.

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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?

思考：其实还是O(m+n)，但是没有另外开辟空间，将标记记录在矩阵首行首列。增加判断首行首列是否要置0即可。

class Solution {
public:
    void setZeroes(vector<vector<int> > &matrix) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
		int m=matrix.size();
		int n=matrix[0].size();
		int i,j;
		bool flag1=false;//第一列是否有0
		bool flag2=false;//第二列是否有0
		for(i=0;i<m;i++)
		{
			if(matrix[i][0]==0) 
			{
				flag1=true;
				break;
			}
		}
		for(i=0;i<n;i++)
		{
			if(matrix[0][i]==0) 
			{
				flag2=true;
				break;
			}
		}
		//若此数为0,则行首列首置0
		for(i=1;i<m;i++)
		{
			for(j=1;j<n;j++)
			{
				if(matrix[i][j]==0)
				{
					matrix[i][0]=0;
					matrix[0][j]=0;
				}
			}
		}
		//列行中有0，则此数置0
		for(i=1;i<m;i++)
		{
			for(j=1;j<n;j++)
			{
				if(matrix[i][0]==0||matrix[0][j]==0)
					matrix[i][j]=0;
			}
		}
		//判断首行首列是否需要置0
		if(flag1)
		{
			for(i=0;i<m;i++)
				matrix[i][0]=0;
		}
		if(flag2)
		{
			for(j=0;j<n;j++)
				matrix[0][j]=0;
		}
    }
};