hdu 1272 判断所给的图是不是生成树 (并查集)

判断所给的图是不是生成树，如果有环就不是，如果没环但连通分量大于1也不是

find函数 用递归写的话 会无限栈溢出 Orz
要加上那一串 手动扩栈

Sample Input
6 8 5 3 5 2 6 4
5 6 0 0

8 1 7 3 6 2 8 9 7 5
7 4 7 8 7 6 0 0

3 8 6 8 6 4
5 3 5 6 5 2 0 0

-1 -1

Sample Output
Yes
Yes
No

 # include <iostream>
 # include <cstdio>
 # include <cstring>
 # include <algorithm>
 # include <cmath>
 # include <queue>
 # define LL long long
 #pragma comment(linker, "/STACK:1024000000,1024000000")
 using namespace std ;

 const int MAXN=;
 int F[MAXN];
 bool vis[MAXN] ;
 int save[MAXN] ;
 bool flag ;
 int find(int x)//找x的祖先结点
 {
     if(F[x]==x) return x;
     return F[x]=find(F[x]);
 }
 void bing(int u,int v)
 {
     int t1=find(u);
     int t2=find(v);
     if(t1!=t2) F[t1]=t2;
     else flag =  ; //有环
 }
 int main()
 {
     //freopen("in.txt","r",stdin) ;
     int u , v ;
     while(scanf("%d %d" , &u , &v) != EOF)
     {
         if (u == - && v == -)
             break ;
         if (u ==  && v == )
         {
             printf("Yes\n") ;
             continue ;
         }
          int i ;
          for(i=;i<MAXN;i++)
          {
              F[i]=i;
          }
         memset(vis ,  , sizeof(vis)) ;
         F[u] = v ;
         int l =  ;
         flag =  ;
         if (!vis[u])
         {
             vis[u] =  ;
             save[l++] = u ;
         }
         if (!vis[v])
         {
             vis[v] =  ;
             save[l++] = v ;
         }
         while(scanf("%d %d" , &u , &v))
         {
             if (u ==  && v == )
                break ;
             if (flag)
                 continue ;
             if (!vis[u])
         {
             vis[u] =  ;
             save[l++] = u ;
         }
             if (!vis[v])
         {
             vis[v] =  ;
             save[l++] = v ;
         }
             bing(u,v) ;
         }
         int res =  ; //连通分量
         for (i =  ; i < l ; i++)
             if (F[save[i]] == save[i])
                 res++ ;
         if (res >=  || flag == )
             printf("No\n") ;
         else
             printf("Yes\n") ;
     }
     return ;
 }