小希的迷宫---hdu1272

http://acm.hdu.edu.cn/showproblem.php?pid=1272

 #include<stdio.h>
 #include<string.h>
 #include<iostream>
 #include<algorithm>
 #include<math.h>
 #define N 100010
 #define INF 0xfffffff
 using namespace std;

 int f[N],vis[N];

 int Find(int x)
 {
     if(x!=f[x])
         f[x]=Find(f[x]);
     return f[x];
 }

 int main()
 {
     int a, b, pa, pb, flag, i;
     while(scanf("%d%d",&a,&b),a!=-||b!=-)
     {
         for(i=;i<N;i++)
             f[i]=i;
         memset(vis,,sizeof(vis));
         flag=;
         if(a==&&b==)
         {
             printf("Yes\n");//空树也是树；
             continue;
         }
         vis[a] = vis[b] = ;//说明此点出现过；
         pa = Find(a);
         pb = Find(b);
         if(pa != pb)
             f[pb] = pa;
         else
             flag = ;
         while(scanf("%d%d", &a, &b), a+b)
         {
             vis[a] = vis[b] = ;
             pa = Find(a);
             pb = Find(b);
             if(pa != pb)
                 f[pb]=pa;
             else
                 flag=;
         }
         int m=;
         for(i=; i<N; i++)
         {
             if(vis[i]== && f[i]==i)//只能有一个父节点是本身
             {
                 m++;
                 if(m>)
                 {
                     flag=;break;
                 }
             }
         }
         if(flag==)
             printf("No\n");
         else
             printf("Yes\n");
     }
     return ;
 }