Books Exchange (hard version)（记忆搜索）

给书的过程形成一个循环，每个独立循环内的每个人的书回到自己手中的时间相同

#include<iostream>
#include<cstdio>
#include<cstring>

using namespace std;
const int maxn = 2e5+10;

int a[maxn],ans[maxn],book[maxn];


int dfs(int i,int st){
	book[i] = 1;
	if(book[a[i]]){
		return ans[i] = st;
	}
	return ans[i] = dfs(a[i],st+1);
}

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