Sorting

input/code.cpp: In function 'void rec(std::vector<long long int>)':
input/code.cpp:11:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < v.size()-1; i++) {
                     ~~^~~~~~~~~~~~
input/code.cpp:12:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (int j = i+2; j < v.size()-1; j++) {
                           ~~^~~~~~~~~~~~
input/code.cpp:14:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
             for (int k = 0; k < v.size(); k++) to.push_back(v[k]);
                             ~~^~~~~~~~~~

#include <bits/stdc++.h>

#define int long long

using namespace std;

set<vector<int>> vis;
void rec(vector<int> v) {
    if (vis.count(v) != 0) return;
    vis.insert(v);
    for (int i = 0; i < v.size()-1; i++) {
        for (int j = i+2; j < v.size()-1; j++) {
            vector<int> to;
            for (int k = 0; k < v.size(); k++) to.push_back(v[k]);
            swap(to[i],to[i+1]);
            swap(to[j],to[j+1]);
            rec(to);
        }
    }
}

signed main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    int t;
    cin >> t;
    while (t--) {
        int n;
        cin >> n;
        bool sorted = true;
        int a[n];
        for (int i = 0; i < n; i++) cin >> a[i];
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < i; j++) {
                if (a[i]<a[j]) {
                    sorted = false;
                }
            }
        }
        if (n <= 3) {
            if (sorted) cout << "YES\n";
            else cout << "NO\n";
            continue;
        }
        if (n == 4) {
            if (sorted || (a[0] == 3 && a[1] == 4 && a[2] == 1 && a[3] == 2)) cout << "YES\n";
            else cout << "NO\n";
            continue;
        }
        vector<int> v;
        for (int i = 1; i <= n; i++) v.push_back(i);
        /*rec(v);
        for (vector<int> x : vis) {
            for (int i : x) cout << i << ' ';
            cout << '\n';
            int inv = 0;
            for (int i = 0; i < n; i++) {
                for (int j = 0; j < i; j++) {
                    if (x[i]<x[j]) inv++;
                }
            }
            cout << "Inv = " << inv << '\n';
        }*/
        int inv = 0;
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < i; j++) {
                if (a[i]<a[j]) inv++;
            }
        }
        if (inv%2==0) cout <<"YES\n";
        else cout << "NO\n";
    }
}
/*
1
5
1 2 3 4 5

*/

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