#include <bits/stdc++.h>
using namespace std;
long long int sqr(long long int x) { return x * x; }
inline long long int add(long long int a, long long int b) {
  long long int c = a + b;
  if (c >= 1000000007) c -= 1000000007;
  return c;
}
inline long long int mul(long long int a, long long int b) {
  return (a * 1ll * b) % 1000000007;
}
inline long long int sub(long long int a, long long int b) {
  long long int c = a - b;
  if (c < 0) c += 1000000007;
  return c;
}
const int nax = 1000 * 1000 + 10;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  auto ok = [](vector<int> &v, int pos) {
    swap(v[pos + 1], v[pos + 2]);
    swap(v[pos], v[pos + 1]);
  };
  int t;
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    vector<int> v(n);
    vector<pair<int, int>> x(n);
    for (int i = 0; i < n; ++i) {
      cin >> v[i];
      x[i] = {v[i], i};
    }
    sort(x.begin(), x.end());
    for (int i = 0; i < n; ++i) {
      v[x[i].second] = i;
    }
    int cnt = 0;
    for (int i = 0; i < n; ++i) {
      for (int j = i + 1; j < n; ++j) {
        cnt += (v[j] < v[i]);
      }
    }
    if (cnt & 1) {
      for (int i = 0; i < n - 1; ++i) {
        if (x[i].first == x[i + 1].first) {
          swap(v[x[i].second], v[x[i + 1].second]);
          break;
        }
      }
    }
    vector<int> ans;
    for (int i = 0; i < n - 2; ++i) {
      int pos = min_element(v.begin() + i, v.end()) - v.begin();
      while (pos > i + 1) {
        ok(v, pos - 2);
        ans.push_back(pos - 2);
        pos -= 2;
      }
      if (pos != i) {
        ok(v, i);
        ok(v, i);
        ans.push_back(i);
        ans.push_back(i);
      }
    }
    for (int i = 0; i < 3; ++i) {
      if (is_sorted(v.begin(), v.end())) break;
      ok(v, n - 3);
      ans.push_back(n - 3);
    }
    if (!is_sorted(v.begin(), v.end())) {
      cout << -1 << "\n";
    } else {
      cout << ans.size() << "\n";
      for (int i = 0; i < ans.size(); ++i) cout << ans[i] + 1 << " ";
      cout << "\n";
    }
  }
  return 0;
}
