Set Matrix Zeros

LeetCode #73

Description:

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?

Example:

Note

Idea:

用第一行和第一列来存储0，然后用两个bool来记录第一行和第一列里有没有0.

time: O(mn), Space: O(1)

Code:

class Solution {
public:
    void setZeroes(vector<vector<int>>& matrix) {
        if(matrix.empty()) return;

        int m=matrix.size();
        int n=matrix[0].size();
        bool row_zero=false;
        bool column_zero=false;

        for(int i=0; i<m; ++i){
            if(matrix[i][0]==0){
                column_zero=true;
                break;
            }
        }
        for(int j=0; j<n; ++j){
            if(matrix[0][j]==0){
                row_zero=true;
                break;
            }
        }

        for(int i=1; i<m; ++i){
            for(int j=1; j<n; ++j){
                if(matrix[i][j]==0){
                    matrix[i][0]=0;
                    matrix[0][j]=0;
                }
            }
        }

        for(int i=1; i<m; ++i){
            for(int j=1; j<n; ++j){
                if(matrix[i][0]==0 || matrix[0][j]==0){
                    matrix[i][j]=0;
                }
            }

        }


        if(row_zero){
            for(int j=0; j<n; ++j){
                matrix[0][j]=0;
            }
        }
        if(column_zero){
            for(int i=0; i<m; ++i){
                matrix[i][0]=0;
            }
        }        

    }
};