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 ;

 }