#include <bits/stdc++.h>
using namespace std;
const int maxn = 2e6 + 10;
const int inf = 0x3f3f3f3f;
const int M = 1e9 + 7;
long long a[maxn];
vector<int> ans;
int n;
void move(int i) {
  ans.push_back(i);
  int t = a[i + 1];
  a[i + 1] = a[i];
  a[i] = a[i - 1];
  a[i - 1] = t;
}
int main() {
  int t;
  cin >> t;
  while (t--) {
    cin >> n;
    ans.clear();
    for (int i = (0); i < (n); i++) cin >> a[i];
    for (int i = (0); i < (n - 2); i++) {
      int k = i;
      for (int j = (i + 1); j < (n); j++) {
        if (a[k] > a[j]) k = j;
      }
      if (k == i) continue;
      while (k - i > 1) {
        move(k - 1);
        k -= 2;
      }
      if (k - i == 1) move(k);
      k++;
      if (k - i == 2) move(k - 1);
      k -= 2;
    }
    if (a[n - 2] > a[n - 1]) {
      int p = -1, pp;
      for (int i = (0); i < (n - 1); i++) {
        if (a[i] == a[i + 1]) {
          p = i + 1;
        }
      }
      pp = p - 1;
      if (p == -1) {
        if (a[n - 3] == a[n - 1]) {
          p = n - 1;
          pp = n - 3;
        } else {
          cout << -1 << endl;
          continue;
        }
      }
      while (n - 1 - p > 2) {
        move(p + 1);
        p++;
        move(p);
        p++;
      }
      if (n - 1 - p == 2)
        move(p + 1), p++;
      else if (n - 1 - p == 1)
        move(p), p++;
      while (p - pp > 1) {
        move(p - 1);
        p -= 2;
      }
      if (p - pp == 1) move(p);
      p++;
      if (p - pp == 2) move(p - 1);
      p -= 2;
    }
    cout << (int)(ans).size() << endl;
    for (int x : ans) cout << x << ' ';
    cout << endl;
  }
}
