#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
ll power(ll x, ll y);
const ll MOD = 1000000007;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int t;
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    int arr[n + 5];
    for (int i = 1; i <= n; i++) cin >> arr[i];
    vector<int> res;
    for (int i = 1; i <= n; i++) {
      for (int j = 1; j <= n - 2; j++) {
        if (arr[j] > arr[j + 1]) {
          swap(arr[j], arr[j + 2]);
          swap(arr[j], arr[j + 1]);
          res.emplace_back(j);
          res.emplace_back(j);
        } else if (arr[j + 1] > arr[j + 2]) {
          swap(arr[j], arr[j + 1]);
          swap(arr[j], arr[j + 2]);
          res.emplace_back(j);
        }
      }
    }
    int flag = 0;
    for (int i = 2; i <= n; i++)
      if (arr[i] < arr[i - 1]) flag = 1;
    if (flag)
      cout << -1 << "\n";
    else {
      cout << res.size() << "\n";
      for (auto i : res) cout << i << "\n";
      cout << "\n";
    }
  }
}
ll power(ll x, ll y) {
  ll res = 1;
  x %= MOD;
  while (y > 0) {
    if (y & 1) res = (res * x) % MOD;
    y = y >> 1, x = (x * x) % MOD;
  }
  return res;
}
