为什么会wa2个.....

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

int n,p=0;
int map[200001];
int ru[200001];
int sum[200001];
int flag[200001];

int main()
{
	cin>>n;
	int minn=999999;
	for(int i=1;i<=n;i++)
	{
		scanf("%d",&map[i]);
		ru[map[i]]++;
	}
	for(int i=1;i<=n;i++)
	{
		if(ru[i]==0) 
		{
			ru[map[i]]--;
			int a=map[i];
			while(ru[a]==0)
			{
				ru[map[a]]--;
				flag[a]=1;
				a=map[a];
			}
			flag[i]=1;
		}
	}
	for(int i=1;i<=n;i++)
	{
		if(flag[i]==1)
		{
			sum[i]=999999;
			continue;
		}
		if(flag[i]!=1)
		{
			int fa=i;
			for(int j=1;j<=n;j++)
			{
				sum[i]++;
				flag[fa]=1;
				fa=map[fa];
				if(fa==i) break;
			}
			if(sum[i]<=minn) minn=sum[i];
		}
	}
	cout<<minn<<endl;
}