uva 1160

 

并查集判断图上是否有环

 

#include <iostream>
#include <algorithm>
using namespace std;
 const int N=1e5+4;
 int fa[N];
 int find(int x){
 	return x==fa[x]?x:fa[x]=find(fa[x]);
 }
 signed main(){
 	int i,j,x,y;
 	while(scanf("%d",&x)==1){
	 int cnt=0;
 	for(i=1;i<=N;i++) fa[i]=i;
 	while(x!=-1){
 		scanf("%d",&y);
 		int fx=find(x),fy=find(y);
 		if(fx==fy) cnt++;
		else fa[fx]=fy;
		
		scanf("%d",&x);
	 }
	printf("%d\n",cnt);
	}
 }