#include <bits/stdc++.h>
using namespace std;
int main() {
  auto make = [](vector<int> &a, int pos) {
    swap(a[pos + 1], a[pos + 2]);
    swap(a[pos], a[pos + 1]);
  };
  int t;
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    vector<int> a(n);
    vector<pair<int, int>> res(n);
    for (int i = 0; i < n; ++i) {
      cin >> a[i];
      res[i] = {a[i], i};
    }
    sort(res.begin(), res.end());
    for (int i = 0; i < n; ++i) {
      a[res[i].second] = i;
    }
    int cnt = 0;
    for (int i = 0; i < n; ++i) {
      for (int j = i + 1; j < n; ++j) {
        cnt += a[j] < a[i];
      }
    }
    if (cnt & 1) {
      for (int i = 0; i < n - 1; ++i) {
        if (res[i].first == res[i + 1].first) {
          swap(a[res[i].second], a[res[i + 1].second]);
          break;
        }
      }
    }
    vector<int> ans;
    for (int i = 0; i < n - 2; ++i) {
      int pos = min_element(a.begin() + i, a.end()) - a.begin();
      while (pos > i + 1) {
        make(a, pos - 2);
        ans.push_back(pos - 2);
        pos -= 2;
      }
      if (pos != i) {
        make(a, i);
        make(a, i);
        ans.push_back(i);
        ans.push_back(i);
        pos = i;
      }
    }
    if (!is_sorted(a.begin(), a.end())) {
      cout << -1 << endl;
    } else {
      cout << ans.size() << endl;
      for (auto it : ans) cout << it + 1 << " ";
      cout << endl;
    }
  }
  return 0;
}
