1 #include <iostream>
  2 #include <cstdio>
  3 #include <cstring>
  4 #include <cstdlib>
  5 #include <cmath>
  6 #include <cctype>
  7 #include <algorithm>
  8 using namespace std;
  9 const int MAXN = 1e5 + 3;
 10 int pre[MAXN];    //储存父节点
 11 bool bol[MAXN];   //这个点是否出现过
 12 int flag1 = 1;   //代表入度是否满足是一个树
 13 int flag2 =  1;  //代表是否成环。
 14 int cnt[MAXN];   //记录出现的点的入度
 15
 16 int Find(int x)
 17 {
 18     int r = x;
 19     while(pre[r] != r)
 20     {
 21         r = pre[r];
 22     }
 23     int i = x,j;
 24     while(pre[i] != r)
 25     {
 26         j = i;
 27         i = pre[i];
 28         pre[j] = r;
 29     }
 30     return r;
 31 }
 32
 33 void Mix(int a,int b)
 34 {
 35     int x = Find(a);
 36     int y = Find(b);
 37     if(x > y)
 38     {
 39         pre[x] = y;
 40     }
 41     if(x < y)
 42     {
 43         pre[y] = x;
 44     }
 45 }
 46
 47
 48 int Search()
 49 {
 50     int cnt = 0;
 51     for(int i = 1; i <= MAXN; i++)
 52     {
 53         if(bol[i])
 54             if(pre[i] == i)
 55                 cnt++;
 56     }
 57     return cnt;
 58 }
 59
 60 int main()
 61 {
 62     int M,N;
 63     flag1 = 1;        //一大堆初始化0.0
 64     flag2 = 1;
 65     for(int i = 1; i <= MAXN; i++)
 66     {
 67         pre[i] = i;
 68         bol[i] = false;
 69     }
 70     memset(cnt,0,sizeof(cnt));
 71     int kas = 1;
 72     while(~scanf("%d%d",&M,&N)&&(M != -1 || N != -1))
 73     {
 74         bol[M] = true;
 75         bol[N] = true;
 76         cnt[N]++;
 77         if(M != 0 && N != 0)
 78         {
 79             int m = Find(M);
 80             int n = Find(N);
 81             if(m == n)
 82                 flag2 = 0;          //出现了环
 83             Mix(M,N);
 84         }
 85         else
 86         {
 87             int single = Search(); //根节点的个数
 88             for(int i = 1; i <= MAXN;i++)
 89             {
 90                 if(cnt[i] > 1)
 91                     flag1 = 0;        //有入度大于一的出现
 92             }
 93             if(single < 2 && flag1 && flag2) printf("Case %d is a tree.\n",kas++);   //三个条件都满足
 94             else printf("Case %d is not a tree.\n",kas++);
 95             flag1 = 1;
 96             flag2 = 1;
 97             for(int i = 1; i <= MAXN; i++)
 98             {
 99                 pre[i] = i;
100                 bol[i] = false;
101             }
102             memset(cnt,0,sizeof(cnt));
103         }
104     }
105     return 0;
106 }