Sorting

#include<bits/stdc++.h>
using namespace std;

int32_t main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int t; cin >> t;
  while (t--) {
    int n; cin >> n;
    vector<int> a(n), b(n);
    for (int i = 0; i < n; i++) {
      cin >> a[i];
      b[i] = i + 1;
    }
    int ok = 0;
    if (n <= 3) {
      ok = a == b;
    }
    else if (n == 4) {
      if (a == b || (a == vector<int>({3, 4, 1, 2}))) {
        ok = 1;
      }
    }
    else {
      int inv = 0;
      for (int i = 0; i < n; i++) {
        for (int j = i + 1; j < n; j++) {
          inv += a[i] > a[j];
        }
      }
      ok = inv % 2 == 0;
    }
    if (ok) {
      cout << "YES\n";
    }
    else {
      cout << "NO\n";
    }
  }
  return 0;
}

Test 1

Group: 1, 2

Verdict: ACCEPTED

Test 2

Group: 2

Verdict: ACCEPTED

Test 3

Group: 1, 2

Verdict: ACCEPTED

Test 4

Group: 1, 2

Verdict: ACCEPTED