Leetcode-73. Set Matrix Zeroes

前言：为了后续的实习面试，开始疯狂刷题，非常欢迎志同道合的朋友一起交流。因为时间比较紧张，目前的规划是先过一遍，写出能想到的最优算法，第二遍再考虑最优或者较优的方法。如有错误欢迎指正。博主首发优快云，mcf171专栏。

博客链接：mcf171的博客

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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?

暂时没想出不用额外空间的方法。使用了O（m+n）的额外空间。 Your runtime beats 26.63% of java submissions.

public class Solution {
    public void setZeroes(int[][] matrix) {

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

        for( int i = 0 ; i < m+n; i++){

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

    }
}