学步园

Set Matrix Zeroes

Apr 6 '12

4561 / 10629

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?

public class Solution {
    public void setZeroes(int[][] matrix) {
        
        if(matrix ==null) return;
        int m = matrix .length;
        if(m>0){
            int n = matrix[0].length;
            boolean row = false, col = false;
            
            for(int i=0;i<m;i++){
                if(matrix[i][0]==0){
                    col = true;
                    break;
                }
            }
            for(int j=0;j<n;j++){
                if(matrix[0][j]==0){
                    row = 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;  //不用其他值来标示，因为题目没有说清楚其他值的范围
                        matrix[0][j]=0;
                    }
                    
                }
            }
            
            for(int i=1;i<m;i++){  //必须从1开始！，很容易看不出来问题....
                if(matrix[i][0]==0){
                    for(int j=1;j<n;j++)
                        matrix[i][j]=0;
                }
            }
            
            for(int j=1;j<n;j++){  //必须从1开始！
                if(matrix[0][j]==0){
                    for(int i=1;i<m;i++)
                        matrix[i][j]=0;
                }
            }
            
            if(row){
                for(int j=0;j<n;j++)
                    matrix[0][j]=0;
            }
            
            if(col){
                for(int i=0;i<m;i++)
                    matrix[i][0]=0;
            }
            
        }
        
    }
}