> #define maxn 50002
> #include<stdio.h>
> #include<string.h>
> long int  n,m,father[maxn],rank[maxn];
> long int find(long int a)
>  {long int r,q;
>   r=a;
>   while (r!=father[r]) r=father[r];
>   while (a!=r) {q=father[a];father[a]=r;a=q;}
>   return(r);
>  }
> void main()
> { long int num=0,x1,y1,i,x,y,sum;
>   scanf("%ld %ld",&n,&m);
>   while (n!=0)
>    {
>     sum=n;num+=1;
>     memset(father,0,sizeof(father));memset(rank,0,sizeof(rank));
>     for (i=1;i<=n;i++) rank[i]=1;
>     for (i=1;i<=n;i++) father[i]=i;
>     for (i=1;i<=m;i++)
>      {
>        scanf("%ld %ld",&x,&y);
>        if (x!=y)
> 	   {
> 	    x1=find(x);y1=find(y);
> 	    if (x1!=y1)
> 			{ if (rank[x1]>rank[y1]) {father[y1]=x1;rank[x1]+=rank[y1];}
> 			 else {father[x1]=y1;rank[y1]+=rank[x1];}
> 		    sum=sum-1;;
> 	       }
>        }
>      }
>     printf("Case %ld: %ld\n",num,sum);
>     scanf("%ld %ld",&n,&m);
>    }
> }
才用了路径压缩和启发式合并技术