#include <bits/stdc++.h>
using namespace std;
void solve() {
  long long n;
  cin >> n;
  long long a[n], b[n];
  set<long long> s;
  for (long long i = 0; i < n; i++) {
    cin >> a[i];
    s.insert(a[i]);
    b[i] = a[i];
  }
  vector<long long> v;
  sort(b, b + n);
  for (long long i = 0; i < n; i++) {
    if (a[i] == b[i])
      ;
    else {
      long long in, cnt = 1;
      for (long long j = i + 1; j < n; j++) {
        if (a[j] == b[i]) {
          in = j;
          break;
        } else {
          cnt++;
        }
      }
      if (in == n - 1 && i == n - 2) {
        if (s.size() == n) {
          cout << -1;
          return;
        }
        if (a[n - 1] == a[n - 3]) {
          v.push_back(n - 2);
          break;
        }
        for (long long j = n - 3; j >= 1; j -= 2) {
          v.push_back(j);
          v.push_back(j);
          v.push_back(j + 1);
          v.push_back(j + 1);
          if (a[j] == a[j - 1]) {
            break;
          }
          if (a[j - 1] == a[j - 2]) {
            v.push_back(j - 1);
            break;
          }
        }
        break;
      }
      while (cnt > 1) {
        swap(a[in], a[in - 2]);
        swap(a[in], a[in - 1]);
        in -= 2;
        cnt -= 2;
        v.push_back(in + 1);
      }
      if (cnt == 1) {
        swap(a[i], a[i + 1]);
        swap(a[i + 1], a[i + 2]);
        v.push_back(i + 1);
        v.push_back(i + 1);
      }
    }
  }
  cout << v.size() << endl;
  for (long long i = 0; i < v.size(); i++) cout << v[i] << " ";
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  long long tt = 1;
  cin >> tt;
  while (tt--) {
    solve();
    cout << endl;
  }
}
