hdu 1325数据弱

#include<stdio.h>//判断是否有环，判断是否有点，判断是否是一个父节点
#include<string.h>
#define N 1000000
int pre[N+10],dis[N+10];
int find(int n ) {
if(pre[n]!=n)
return pre[n]=find(pre[n]);
return pre[n];
}
int main() {
int n,m,i,a,b,j,cnt,flag,f1,f2,k=0,min,max;
while(scanf("%d%d",&a,&b),a>=00&&b>=0){//判断条件需注意
if(a==0&&b==0) {
printf("Case %d is not a tree. ",++k);//和1272不一样如果没有节点就不是树
continue;
}
for(i=1;i<=N;i++)
pre[i]=i;
f1=find(a);
f2=find(b);
pre[f2]=f1;
dis[a]=dis[b]=1;
min=a>b?b:a;
max=a>b?a:b;
flag=0;
while(scanf("%d%d",&a,&b),a&&b) {
f1=find(a);
f2=find(b);
if(f1==f2)
flag=1;
else
pre[f2]=f1;
dis[a]=dis[b]=1;
min=min<a?min:a;
min=min<b?min:b;
max=max>a?max:a;
max=max>b?max:b;
}
if(flag) {
printf("Case %d is not a tree. ",++k);
continue;
}
cnt=0;
for(i=min;i<=max;i++)
if(pre[i]==i&&dis[i])
cnt++;
if(cnt==1)
printf("Case %d is a tree. ",++k);
else
printf("Case %d is not a tree. ",++k);
}
return 0;
}