#include <bits/stdc++.h>
using namespace std;
const long long MAX = 1e6 + 8;
const long long MOD = 1e9 + 7;
const long long sz = 1e5 + 5;
void f_io() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ;
}
int32_t main() {
  f_io();
  long long tc = 1;
  cin >> tc;
  auto rotate = [](vector<long long>& v, long long ind) {
    swap(v[ind + 1], v[ind + 2]);
    swap(v[ind], v[ind + 1]);
  };
  while (tc--) {
    long long n;
    cin >> n;
    vector<pair<long long, long long>> val;
    for (long long i = 0, a; i < n; i++) {
      cin >> a;
      val.push_back({a, i});
    }
    sort(begin(val), end(val));
    vector<long long> permutation(n);
    long long inversion_cnt = 0;
    for (long long i = 0; i < n; i++) permutation[val[i].second] = i;
    for (long long i = 0; i < n; i++) {
      for (long long j = i + 1; j < n; j++) {
        if (permutation[j] < permutation[i]) inversion_cnt++;
      }
    }
    long long poss = 1;
    if (inversion_cnt & 1) {
      poss = 0;
      for (long long i = 0; i < n - 1; i++) {
        if (val[i].first == val[i + 1].first) {
          swap(permutation[val[i].second], permutation[val[i + 1].second]);
          poss = 1;
          break;
        }
      }
    }
    vector<long long> ret;
    if (!poss) {
      cout << "-1"
           << "\n";
      continue;
    }
    for (long long i = 0; i < n - 2; i++) {
      long long ind = min_element(begin(permutation) + i, end(permutation)) -
                      permutation.begin();
      while (ind > i + 1) {
        rotate(permutation, ind - 2);
        ret.push_back(ind - 2);
        ind -= 2;
      }
      if (ind != i) {
        rotate(permutation, i);
        ret.push_back(i);
        ret.push_back(i);
        rotate(permutation, i);
        ind = i;
      }
    }
    for (long long i = 0; i < 3; i++) {
      if (is_sorted(begin(permutation), end(permutation))) break;
      rotate(permutation, n - 3);
      ret.push_back(n - 3);
    }
    if (!is_sorted(begin(permutation), end(permutation)))
      cout << "-1"
           << "\n";
    else {
      cout << ret.size() << "\n";
      for (auto k : ret) cout << k + 1 << " ";
      cout << "\n";
    }
  }
}
