1 #include<stdio.h> 2 #include<algorithm> 3 #include<string.h> 4 #include<iostream> 5 using namespace std; 6 const int M=100010; 7 int fa[M],vis[M],root[M]; 8 int fin(int x){ 9 return fa[x]==x?fa[x]:fa[x]=fin(fa[x]);10 }11 int  unin(int x,int y){12 return fa[fin(y)]=fin(x);13 }14 void init(int n){15 for(int i=0;i<n;i++){16     fa[i]=i;17 }18 memset(vis,0,sizeof(vis));19 memset(root,0,sizeof(root));20 }21 int main()22 {23     int a,b;24     int cas=1;int flag=1;25     init(M);26     while(~scanf("%d%d",&a,&b)){27         if(a<0||b<0)break;28 29 30         if(a==0&&b==0){31             int k=0;32             for(int i=1;i<M;i++){33                 if(vis[i]&&fa[i]==i){34                     k++;35                 }36                 if(root[i]>1){37                     flag=0;38                     break;39 40                 }41 42             }43             if(k>1)flag=0;44             if(flag)printf("Case %d is a tree.\n",cas++);45             else printf("Case %d is not a tree.\n",cas++);46             flag=1;47             init(M);48             continue;49         }50         if(a!=b&&fin(a)==fin(b)){51             flag=0;52         }53         else {54             vis[a]=1;55             vis[b]=1;56             root[b]++;57             unin(a,b);58         }59     }60     return 0;61 }