Sorting

#include <bits/stdc++.h>
 
#define pb push_back
#define int long long
#define all(x) x.begin(), x.end()
#define ld long double
using namespace std;
 
 
signed main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    int t;
    cin >> t;
    while (t--) {
        int n;
        cin >> n;
        vector<int> a(n);
        for (int i = 0; i < n; i++) cin >> a[i];
        if (n <= 4) {
            set<vector<int>> b;
            for (int _ = 0; _ < 1000; _++) {
                int i1 = rand() % n, i2 = rand() % n;
                if (i1 > i2) swap(i1, i2);
                if (i2 < n - 1 && i1 + 1 < i2) {
                    swap(a[i1], a[i2]);
                    swap(a[i1 + 1], a[i2 + 1]);
                }
                b.insert(a);
            }
            vector<int> aa(n);
            for (int i = 0; i < n; i++) aa[i] = 1 + i;
            if (b.find(aa) == b.end()) {
                cout << "NO\n";
            } else {
                cout << "YES\n";
            }
        } else {
            bool ok = true;
            for (int i = 0; i < n; i++) {
                for (int j = i + 1; j < n; j++) {
                    ok ^= (a[i] > a[j]);
                }
            }
            if (ok) {
                cout << "YES\n";
            } else {
                cout << "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