并查集。

#include
     
      #include
      
       using namespace std;const int maxn = 55555;int fa[maxn];int vis[maxn];int n,m,t;void init(){    for(int i = 0; i < n; i++) {fa[i] = i;}    memset(vis,0,sizeof(vis));}int find_father(int u){    return fa[u] == u ? u : fa[u] = find_father(fa[u]);}int main(){    int Case = 1;    while(scanf("%d%d",&n,&m)){        if(!m && !n) break;        init();        for(int i = 0; i < m; i++){            int x,y;            scanf("%d%d",&x,&y);            int fx = find_father(x);            int fy = find_father(y);            fa[fx] = fy;        }        int cnt = 0;        for(int i = 1; i <= n; i++){            int t = find_father(i);            if(!vis[t]){                vis[t] = 1;                cnt ++;            }        }        printf("Case %d: %d\n",Case++,cnt);    }    return 0;}