如果我去年在 考場上 會怎樣呢？

#include <cstdio>
#include <cstring>
#include <iostream>
#include <cstdlib>
using namespace std;

#define MAXN (200020)
int tot = 0;
int first[MAXN], nxt[MAXN], vis[MAXN], useby[MAXN];
struct edge{
    int from, to;
}es[MAXN];

void build(int ff, int tt)
{
    es[++tot] = (edge){ff,tt};
    nxt[tot] = first[ff];
    first[ff] = tot;
}

int
 
 ans = 1e9;
void dfs(int x, int c, int root)
{
    vis[x] = c;
    useby[x] = root;
    for(int i = first[x]; i != -1; i = nxt[i])
    {
        int v = es[i].to;
        if(vis[v])
        {
            if(useby[v] == root) ans = min(ans, c-vis[v]+1);
            continue;
        }
        dfs(v,c+1
 
,root);
    }
}

int main()
{
    int n;
    cin >> n;
    memset(first,-1,sizeof(first));
    for(int i = 1;i <= n; ++ i)
    {
        int t;
        scanf("%d", &t);
        build(i,t);
    }
    for(int i = 1; i <= n; ++ i)
        if(!vis[i])
            dfs(i,1,i);
    cout << ans << '\n'
 
;
    return 0;
}