Noitapeli

#include <iostream>
#include <algorithm>
#include <set>
using namespace std;

#define max(a, b) (((a)>(b))?(a):(b))
#define min(a, b) (((a)<(b))?(a):(b))

long long nCr(int n, int k) {
  long long a = 1;
  for (int i = n; i > max(k, n-k); i--) {
    a *= i;
  }
  for (int i = 2; i <= min(n-k, k); i++) {
    a /= i;
  }
  return a;
}

int main() {
  int n;
  cin >> n;

  set<int> a[n+1];
  
  long long c = nCr(n, 3);
  //cout << c << "\n";
  for (int i = 1; i <= n; i++) {
    int j;
    cin >> j;
    if (a[i].count(j)>0 && a[j].count(i)>0) continue;
    a[i].insert(j);
    a[j].insert(i);
    set<int> ins;
    ins.insert(a[i].begin(), a[i].end());
    ins.insert(a[j].begin(), a[j].end());
    //cout << n-ins.size() << "\n";
    //for (int i : ins) cout << ": " << i << "\n";
    c -= n-ins.size();
  }
  cout << c << "\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: TIME LIMIT EXCEEDED

Test 14

Group: 3

Verdict: ACCEPTED

Test 15

Group: 3

Verdict: ACCEPTED