#include <bits/stdc++.h>
using namespace std;
int fr[200004];
struct cmp {
  bool operator()(int a, int b) const { return a > b; }
};
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ;
  auto make = [](vector<int>& a, int pos) {
    swap(a[pos + 2], a[pos + 1]);
    swap(a[pos + 1], a[pos]);
  };
  int t;
  cin >> t;
  while (t--) {
    int n, i, j, k, l;
    cin >> n;
    vector<int> v(n);
    vector<pair<int, int>> p(n);
    for (i = 0; i < n; i++) {
      cin >> v[i];
      p[i] = {v[i], i};
    }
    sort(p.begin(), p.end());
    for (i = 0; i < n; i++) v[p[i].second] = i;
    int cnt = 0;
    for (i = 0; i < n - 1; i++) {
      for (j = i + 1; j < n; j++)
        if (v[j] < v[i]) cnt++;
    }
    if (cnt & 1) {
      for (i = 0; i < n - 1; i++)
        if (p[i].first == p[i + 1].first) {
          swap(v[p[i].second], v[p[i + 1].second]);
          break;
        }
    }
    vector<int> ans;
    for (i = 0; i < n - 2; i++) {
      int pos = min_element(v.begin() + i, v.end()) - v.begin();
      while (pos > i + 1) {
        make(v, pos - 2);
        ans.push_back(pos - 2);
        pos = pos - 2;
      }
      if (pos != i) {
        make(v, i);
        make(v, i);
        ans.push_back(i);
        ans.push_back(i);
        pos = i;
      }
    }
    for (i = 0; i < 3; i++) {
      if (is_sorted(v.begin(), v.end())) {
        break;
      }
      make(v, n - 3);
      ans.push_back(n - 3);
    }
    if (!is_sorted(v.begin(), v.end())) {
      cout << -1 << "\n";
      continue;
    }
    cout << ans.size() << "\n";
    for (int x : ans) cout << x + 1 << " ";
    cout << "\n";
  }
}
