Noitapeli

#include <iostream>
#include <vector>
using namespace std;
typedef long long ll;
#define N (1<<18)

vector<int> v[N];
ll t[N], yhh[N], hyhh[N];
int  main(){
	long long n; cin >> n;
	ll V = n*(n-1)*(n-2)/6, x=0, x2=0, x3=0;
	for(int i=1; i<=n; ++i){
		int a; cin >> a;
		if(yhh[a]==i) continue;
		yhh[i]=a;
		++x;
		v[i].push_back(a);
		v[a].push_back(i);
		++t[i], ++t[a];
	}
	for(int i=1; i<=n; ++i){
		int u = yhh[i];
		if(u==0) continue;
		--t[u], --t[i];
		x2+=t[u];
		x2+=t[i];
		if(yhh[yhh[u]] ==i ){
			++x3;
			--x2;
		}
		yhh[i]=0;
	}
	//cout << x << " " << x2 << " " << x3 << "\n";
	cout << V-x*(n-2)+x2 << "\n";
}

Test 1

Group: 1

Verdict: ACCEPTED

Test 2

Group: 1

Verdict: ACCEPTED

Test 3

Group: 1

Verdict: ACCEPTED

Test 4

Group: 1

Verdict: ACCEPTED

Test 5

Group: 1

Verdict: ACCEPTED

Test 6

Group: 2

Verdict: ACCEPTED

Test 7

Group: 2

Verdict: ACCEPTED

Test 8

Group: 2

Verdict: ACCEPTED

Test 9

Group: 2

Verdict: ACCEPTED

Test 10

Group: 2

Verdict: ACCEPTED

Test 11

Group: 3

Verdict: ACCEPTED

Test 12

Group: 3

Verdict: ACCEPTED

Test 13

Group: 3

Verdict: ACCEPTED

Test 14

Group: 3

Verdict: ACCEPTED

Test 15

Group: 3

Verdict: ACCEPTED