信息传递

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<math.h>
#include<queue>
#include<vector>
using namespace std;
int n;
int to[210000],dfn[210000],ans=999999,cnt=0,cntt=0,t[210000]; 
void dfs(int x)
{
    t[x]=cntt;
    dfn[x]=++cnt;    
    if(dfn[to[x]])    
    if(cntt==t[to[x]])
    {ans=min(dfn[x]-dfn[to[x]]+1,ans);return ;}
    else    return;
    dfs(to[x]);
    return ;
}
int main()
{
    scanf("%d",&n);
    int c;
    for(int i=1;i<=n;i++)
        scanf("%d",&c),to[i]=c;
    for(int i=1;i<=n;i++)
    if(!dfn[i])
        cntt++,dfs(i);
    cout<<ans;
    return 0;
}