73. Set Matrix Zeroes (Array)

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

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?

思路：第一行和第一列用来标示该行、该列是否全0，但事先得判断第一行、第一列是否全0=>用两个额外的变量存储

class Solution {
public:
    void setZeroes(vector<vector<int> > &matrix) {
        if(matrix.empty()) return;
        
        bool firstLineZero = false;
        bool firstColumnZero = false;
        if(matrix[0][0]==0){
            firstLineZero = true;
            firstColumnZero = true;
        }
        //the first line
        for(int i = 1; i<matrix[0].size(); i++)
        {
            if(matrix[0][i]!=0) continue;
            firstLineZero = true;
            break;
        }
         //the first column
        for(int i = 1; i<matrix.size(); i++)
        {
            if(matrix[i][0]!=0) continue;
            firstColumnZero = true;
            break;
        }
          
        for(int i = 1; i < matrix.size(); i++)
        {
            for(int j = 1; j<matrix[0].size(); j++)
            {
                if(matrix[i][j] != 0) continue;
                matrix[i][0] = 0;
                matrix[0][j] = 0;
            }
        }

        for(int i = 1; i<matrix[0].size(); i++)
        {
            if(matrix[0][i]!=0) continue;
            for(int j = 1; j<matrix.size(); j++)
            {
                matrix[j][i]=0;
            }
        }
        for(int i = 1; i<matrix.size(); i++)
        {
            if(matrix[i][0]!=0) continue;
            for(int j = 1; j<matrix[0].size(); j++)
            {
                matrix[i][j]=0;
            }
        }
        
        if(firstLineZero)
        {
            for(int i = 0 ; i< matrix[0].size(); i++)
            {
                matrix[0][i] = 0;
            }
        }
        if(firstColumnZero)
        {
            for(int i = 0 ; i< matrix.size(); i++)
            {
                matrix[i][0] = 0;
            }
        }
    }
};