历届真题 小朋友崇拜圈【第九届】【省赛】【C组】——【C++】【C】【Java】【Python】四种语言解法

#include<iostream>
#include<algorithm>
using namespace std;
int vis[100009];
int ans;
int indug[100009];
int vis1[100009];
void dfs(int n,int qi,int l)
{
	if(vis[n]==qi)
	{
		ans=max(ans,l); 
		return;
	}
	vis1[vis[n]]=1;
	dfs(vis[n],qi,l+1);
}
int main()
{
	int n;
	cin>>n;
	for(int i=1;i<=n;i++)
	{
		cin>>vis[i];
		indug[vis[i]]++;
	}
	for(int i=1;i<=n;i++)
	{
		if(vis1[i]==0&&indug[i]!=0)
		{
			vis1[i]=1;
			dfs(i,i,1);
		}
	}
	cout<<ans;
	return 0;
}

#include<stdio.h>
#define MAX 100005
int state[MAX];
int arr[MAX];
int ans;
void dfs(int k,int step){
	if(state[arr[k]]!=0){
		if(step-state[arr[k]]+1>ans)ans=step-state[arr[k]]+1;
		return;
	}
	state[k]=step;
	dfs(arr[k],step+1);
}
int main()
{
	int n;
	scanf("%d",&n);
	int i;
	for(i=1;i<=n;i++)scanf("%d",&arr[i]);
	for(i=1;i<=n;i++)dfs(i,1);
	printf("%d",ans);
	return 0;
}

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.StreamTokenizer;

public class Main {
	public static void main(String[] args) throws IOException {
		n = nextInt();
		isWorship = new boolean[n+1];
		a = new int[n+1];
		for(int i = 1;i <= n;i++) {
			int x = nextInt();
			isWorship[x] = true;
			a[i] = x;
		}
		for(int i = 1;i <= n;i++) {
			if(isWorship[i]) {
				start = i;
				dfs(i,0);
			}
		}
		System.out.println(max);
	}
	private static void dfs(int x, int s) {
		if(x > n) return;
		if(x == start && s != 0) {
			max = Math.max(s, max);
			return;
		}
		if(!isWorship[x]) {
			return;
		}
		isWorship[x] = false;
		dfs(a[x],s+1);
	}
	static int nextInt() throws IOException {
		st.nextToken();
		return (int) st.nval;
	}
	static StreamTokenizer st = new StreamTokenizer(new BufferedReader(new InputStreamReader(System.in)));
	static int start,a[],n,max;
	static boolean[] isWorship;
}

from collections import defaultdict

n=int(input())
l=[0]+list(map(int,input().split()))
vis=defaultdict(int)
ans=0

for i in range(1,n+1):
  if not vis[i]:
    now=l[i]
    k=1
    vis[i]=k
    while not vis[now]:
      k+=1
      vis[now]=k
      now=l[now]
    ans=max(ans,k-vis[now]+1)
print(ans)