【P2661】信息传递【并查集】查找最小环

/*
信息传递 P2661
有向图最小环
algorithm:并查集
by sbn
2018-1-14
*/
#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<string>
#include<cmath>
#include<algorithm>
using namespace std;
const int MAXN=2e6+10;
int fa[MAXN],dis[MAXN],n,res=2e6;
int getfa(int x){
if (fa[x]!=x){
int last=fa[x];
fa[x]=getfa(fa[x]);
dis[x]+=dis[last];
}
return fa[x];
}
void link(int a,int b){
int x=getfa(a),y=getfa(b);
if (x!=y){
fa[x]=y;
dis[a]=dis[b]+1;
}else res=min(res,dis[a]+dis[b]+1);
return;
}
int main(){
cin>>n;
for (int i=1;i<=n;i++)  fa[i]=i;
for (int i=1;i<=n;i++){
int f;
cin>>f;
link(i,f);
}

cout<<res<<endl;
return 0;
}