#include <iostream>
#include <bits/stdc++.h>
using namespace std;
int main()
{
		int n;
		char poly[55][55];
		cin>>n;
		for(int a=1;a<=n;a++){
			for(int b=1;b<=n;b++){
				char ch
				cin>>ch;
				poly[a][b]=ch-'0';
			}
		}
		bool flag=1;
		for(int a=1;a<n;a++){
			for(int b=1;b<n;b++){
				if(poly[a][b]==0)continue;
				if(poly[a+1][b]||poly[a][b+1])continue;
				flag=0;
				break;
			}
		}
		switch(flag){
			case 1:cout<<"YES"<<endl;
			case 0:cout<<"NO"<<endl;
		}
	return 0;
}

有一个输出的是YES和NO，怎么了，代码有什么问题？？？