POJ2236 Wireless Network-并查集

题目链接 http://poj.org/problem?id=2236

#include<cstdio>
using namespace std;
int n,m;
int pre[50005];
void Init(){
	for(int i = 0;i < n;i++)
		pre[i] = i;
}
int Find(int x){        //找到祖先
	int t = x;
	while(pre[t] != t)
		t = pre[t];
	return t;
}
void Union(int x,int y){            合并
	int xx = Find(x);
	int yy = Find(y);
	if(xx != yy){
		pre[xx] = yy;
	}	
}

int main(){
	int num;
	int first;
	int later;
	while(scanf("%d%d",&n,&m) != EOF){
		if(n == 0 && m == 0)
			break;
		Init();
		for(int i = 1;i <= m;i++){
			scanf("%d",&num);
			scanf("%d",&first);
			for(int j = 2;j <= num;j++){
				scanf("%d",&later);
				Union(first,later);
			} 						
		}
		int sum = 1;
		int flag = Find(0);
		for(int i = 1;i < n;i++){
			if(Find(i) == flag)
				sum++;			
		}
		printf("%d\n",sum);
	}
	return 0;
}