还是并查集的问题，只是数据要注意：
输入0 0，输出yes
迷宫裂开了输出No
#include <stdio.h>
#define MAXN 100001
int p[MAXN],num[MAXN];
int is(int a)
{
     if ((num[a]==1)&&(a==p[a])) return 0;
     else return 1;
}
int main()
{
     int a,b,pa,pb,i,uc,over=0;
     for (i=0;i<MAXN;i++)
     {
         p[i]=i;
         num[i]=1;
     }
     uc=0;
     while (scanf("%d%d",&a,&b)&&(a!=-1)&&(b!=-1))
     {
         if ((!a)&&(!b))
         {
             if (over || uc>1) printf("No\n");
             else printf("Yes\n");
             for (i=0;i<MAXN;i++)
             {
                 p[i]=i;
                 num[i]=1;
             }
             uc=0;
             over=0;
             continue;
         }
         if (!over)
         {
             pa=a;
             pb=b;
             while (pa!=p[pa]) pa=p[pa];
             while (pb!=p[pb]) pb=p[pb];
         }
         if (pa==pb)
         {
             over=1;
         }else
         if (num[pa]>=num[pb])
         {
             //printf("is(%d)=%d    is(%d)=%d\n",a,is(a),b,is(b));
             if ((!is(a))&&(!is(b)))