Järjestäminen

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

bool solve() {
	int n;
	cin >> n;

	vector<int> a(n);
	for (auto& x : a) cin >> x;

	if (n == 4) return a == vector<int>{1, 2, 3, 4} || a == vector<int>{3, 4, 1, 2};
	if (n < 4) return is_sorted(a.begin(), a.end());

	bool ok = 1;
	for (int i = 0; i < n; ++i) {
		for (int j = i + 1; j < n; ++j) {
			ok ^= a[i] > a[j];
		}
	}

	return ok;
}

int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);

	int t;
	cin >> t;
	for (int i = 0; i < t; ++i) cout << (solve() ? "YES" : "NO") << '\n';
}

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