#include <bits/stdc++.h>
using namespace std;
const long long mod = 1000000007;
const int inf = 1e9 + 10;
const long long INF = 1e18;
const long double EPS = 1e-10;
const int dx[8] = {1, 0, -1, 0, 1, -1, -1, 1};
const int dy[8] = {0, 1, 0, -1, 1, 1, -1, -1};
template <class T>
bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T>
bool chmin(T &a, const T &b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout << fixed << setprecision(25);
  int t;
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    vector<int> a(n);
    for (int i = 0; i < (n); ++i) cin >> a[i];
    vector<pair<int, int>> p(n);
    for (int i = 0; i < (n); ++i) p[i] = {a[i], i};
    sort(p.begin(), p.end());
    int cnt = 0;
    for (int i = 0; i < (n); ++i)
      for (int j = 0; j < (i); ++j)
        if (p[j].second > p[i].second) cnt++;
    for (int i = 0; i < (n - 1); ++i) {
      if (cnt & 1 && p[i].first == p[i + 1].first) {
        swap(p[i], p[i + 1]);
        cnt--;
        break;
      }
    }
    if (cnt & 1) {
      cout << -1 << '\n';
      continue;
    }
    for (int i = 0; i < (n); ++i) a[p[i].second] = i;
    vector<int> ans;
    for (int i = 0; i < (n - 2); ++i) {
      int idx;
      for (int j = (n - 1); j >= 0; --j) {
        if (a[j] == i) {
          idx = j;
          break;
        }
      }
      while (idx - i >= 2) {
        ans.push_back(idx - 2);
        a[idx] = a[idx - 1];
        a[idx - 1] = a[idx - 2];
        a[idx - 2] = i;
        idx -= 2;
      }
      if (idx - i == 1) {
        ans.push_back(idx - 1);
        ans.push_back(idx - 1);
        a[idx] = a[idx + 1];
        a[idx + 1] = a[idx - 1];
        a[idx - 1] = i;
        idx--;
      }
      assert(idx == i);
    }
    cout << ans.size() << '\n';
    for (int x : ans) cout << x + 1 << ' ';
    cout << '\n';
  }
  return 0;
}
