[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;

		}

    }

};