Sorting

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

#include <iostream>
#include <vector>
#include <set>
#include <queue>
#include <algorithm>

using namespace std;

int inv(vector<int> v) {
    int ans = 0;
    for (int i = 0; i < v.size(); i++) {
        for (int j = i + 1; j < v.size(); j++) {
            if (v[i] > v[j]) ans++;
        }
    }
    return ans;
}

int main() {
    ios_base::sync_with_stdio(false); cin.tie(0);
    int t; cin >> t;
    vector<int> spec = {3, 4, 1, 2};
    while (t--) {
        int n; cin >> n;
        vector<int> v;
        while (n--) {
            int x; cin >> x;
            v.push_back(x);
        }
        if (v.size() <= 3) cout << (inv(v) == 0 ? "YES" : "NO") << endl;
        else if (v.size() == 4) cout << (inv(v) == 0 || v == spec ? "YES" : "NO") << endl;
        else cout << (inv(v) % 2 ? "NO" : "YES") << endl;
    }
    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