#include <bits/stdc++.h>
using namespace std;
int main() {
  const int mv = 501;
  int t, iar[mv], ar[mv], par[mv], sar[mv];
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    for (int i = 0; i < n; ++i) {
      cin >> ar[i];
      iar[i] = par[i] = sar[i] = i;
    }
    sort(sar, sar + n, [&](int a, int b) { return ar[a] < ar[b]; });
    vector<int> ana;
    for (int i = 0; i < n - 2; ++i) {
      int ti = iar[sar[i]];
      while (ti > 1 and i != ti and ti - 2 >= i) {
        int tm = par[ti];
        iar[tm] -= 2;
        iar[par[ti - 1]]++;
        iar[par[ti - 2]]++;
        par[ti] = par[ti - 1];
        par[ti - 1] = par[ti - 2];
        par[ti - 2] = tm;
        ti -= 2;
        ana.push_back(ti + 1);
      }
      if (i != ti and ti - 1 == i) {
        ana.push_back(ti);
        ana.push_back(ti);
        iar[par[ti - 1]] += 2;
        iar[par[ti]]--;
        iar[par[ti + 1]]--;
        int tm = par[ti];
        par[ti] = par[ti + 1];
        par[ti + 1] = par[ti - 1];
        par[ti - 1] = tm;
      }
      if (ana.size() > n * n) goto np;
    }
    if (iar[sar[n - 2]] != n - 2) {
      int dv = -1;
      for (int i = n - 1; i > 0; --i)
        if (ar[sar[i]] == ar[sar[i - 1]]) {
          dv = i;
          break;
        }
      if (dv == -1) goto np;
      int k = n - 2;
      while (k >= dv) ana.push_back(k--);
    }
    if (ana.size() > n * n) {
    np:
      cout << "-1\n";
      continue;
    }
    cout << ana.size() << '\n';
    for (int i = 0; i < ana.size(); ++i) cout << ana[i] << " ";
    cout << '\n';
  }
}
