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;
}
}
}
}