并查集，求和0号同集合的点有多少个。

1 #include 
     
       2 #include 
      
        3 #define N 30005 4 int fa[N],num[N]; 5 int find(int a) 6 { 7     if(fa[a] == a) return a; 8     return fa[a] = find(fa[a]); 9 }10 void unin(int a,int b)11 {12     a = find(a);13     b = find(b);14     if(a == b) return;15     if(num[a] >= num[b])16     {17         fa[b] = a;18         num[a] += num[b];19     }20     else21     {22         fa[a] = b;23         num[b] += num[a];24     }25 }26 int main()27 {28     int n,m,i,t,a,b;29     while(scanf("%d%d",&n,&m),n||m)30     {31         for(i = 0; i < n; i++)32         {33             fa[i] = i;34             num[i] = 1;35         }36         while(m--)37         {38             scanf("%d %d",&t,&a);39             while(--t)40             {41                 scanf("%d",&b);42                 unin(a,b);43             }44         }45         printf("%d\n",num[find(0)]);46     }47     return 0;48 }