#include <bits/stdc++.h>
using namespace std;
void swap(vector<int> &v, int j) {
  int temp = v[j];
  v[j] = v[j + 2];
  v[j + 2] = v[j + 1];
  v[j + 1] = temp;
  return;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int T;
  cin >> T;
  for (int t = 0; t < T; ++t) {
    int n;
    cin >> n;
    vector<int> v;
    for (int i = 0; i < n; i++) {
      int a;
      cin >> a;
      v.push_back(a);
    }
    vector<int> indi;
    for (int i = 0; i < n - 1; i++) {
      for (int j = 0; j < n - i - 2; j++) {
        if (v[j] > v[j + 1] && v[j] > v[j + 2]) {
          indi.push_back(j);
          indi.push_back(j);
          swap(v, j);
          swap(v, j);
        } else {
          if (v[j + 1] > v[j + 2]) {
            swap(v, j);
            indi.push_back(j);
          }
        }
      }
    }
    if (v[0] > v[1]) {
      int c = 0;
      if (v[2] == v[0]) {
        indi.push_back(0);
        indi.push_back(0);
        swap(v, 0);
        swap(v, 0);
        c = 1;
      }
      for (int i = 0; i < n; i++) {
        if (v[i] == v[i + 1] && c == 0) {
          c = 1;
          if (i % 2 == 0) {
            int e = 0;
            int o = 1;
            while (e != i) {
              indi.push_back(o);
              swap(v, o);
              indi.push_back(e);
              swap(v, e);
              e += 2;
              o += 2;
            }
          } else {
            int e = 0;
            int o = 1;
            while (o != i) {
              indi.push_back(o);
              swap(v, o);
              indi.push_back(e);
              swap(v, e);
              e += 2;
              o += 2;
            }
            indi.push_back(e);
            swap(v, e);
            indi.push_back(e);
            swap(v, e);
          }
        }
      }
      if (c == 0) {
        cout << -1 << "\n";
        continue;
      }
    }
    cout << indi.size() << "\n";
    for (int i = 0; i < indi.size(); i++) {
      cout << indi[i] + 1 << " ";
    }
    cout << "\n";
  }
}
