判断三元环
#include <cstdio>
#include <iostream>
#include <cstdlib>
#include <cstring>
using namespace std;
#define NN 2001
char a[NN][NN];
int mark[NN], pre[NN];
int start,end;
int n;
/*bool dfs(int prev, int cur) {
mark[cur] = 1;
for (int next=0;next<n;++next)
if (a[cur][next]-'0') {
if (a[next][prev]-'0')
return true;
else if (!mark[next] && dfs(cur,next))
return true;
}
return false;
}*/
bool dfs(int now){
mark[now]=1;
for(int i=0;i<n;i++){
if (a[now][i]-'0') {
if(mark[i]==1)return 1;
if(mark[i]==0 && dfs(i))return 1;
}
}
mark[now]=-1;
return 0;
}
int main () {
int t,T,i,j;
scanf("%d",&T);
for(t=1;t<=T;t++){
printf("Case #%d: ",t);
bool flag=1;
scanf("%d",&n);
for(i=0;i<n;i++)
scanf("%s",a[i]);
memset(mark,0,sizeof(mark));
for (int i=0;i<n;++i)
if (!mark[i] && dfs(i)){
printf("Yes\n");
flag=0;
break;
}
if(flag)
printf("No\n");
}
return 0;
}
