#include <bits/stdc++.h>
template <class T>
inline bool chmax(T& a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T>
inline bool chmin(T& a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
constexpr long long MAX = 5100000;
constexpr long long INF = 1LL << 60;
constexpr int inf = 1000000007;
constexpr long long mod = 1000000007LL;
const long double PI = acos((long double)(-1));
using namespace std;
void f(int idx, vector<int>& a) {
  swap(a[idx + 1], a[idx + 2]);
  swap(a[idx], a[idx + 1]);
}
int find(int s, vector<int>& a) {
  for (int i = 0; i < a.size(); i++)
    if (a[i] == s) return i;
}
void solve() {
  int n;
  scanf("%d", &n);
  vector<int> a(n);
  for (int i = 0; i < n; i++) scanf("%d", &a[i]), a[i]--;
  vector<pair<int, int>> c(n);
  for (int i = 0; i < n; i++) c[i] = {a[i], i};
  sort(c.begin(), c.end());
  for (int i = 0; i < n; i++) a[c[i].second] = i;
  vector<int> res;
  for (int s = 0; s < n - 2; s++) {
    int idx = find(s, a);
    while (idx != s) {
      if (idx - 1 == s)
        f(idx - 1, a), res.emplace_back(idx - 1), idx++;
      else
        f(idx - 2, a), res.emplace_back(idx - 2), idx -= 2;
    }
  }
  auto b = a;
  sort(b.begin(), b.end());
  if (a != b) {
    for (int i = 0; i + 1 < n; i++) {
      if (c[i].first == c[i + 1].first) {
        swap(c[i], c[i + 1]);
        break;
      }
    }
    for (int i = 0; i < n; i++) a[c[i].second] = i;
    vector<int> res;
    for (int s = 0; s < n - 2; s++) {
      int idx = find(s, a);
      while (idx != s) {
        if (idx - 1 == s)
          f(idx - 1, a), res.emplace_back(idx - 1), idx++;
        else
          f(idx - 2, a), res.emplace_back(idx - 2), idx -= 2;
      }
    }
    auto b = a;
    sort(b.begin(), b.end());
    if (a != b)
      puts("-1");
    else {
      printf("%d\n", (int)res.size());
      for (int i = 0; i < res.size(); i++)
        printf("%d%c", res[i] + 1, " \n"[i + 1 == res.size()]);
    }
  } else {
    printf("%d\n", (int)res.size());
    for (int i = 0; i < res.size(); i++)
      printf("%d%c", res[i] + 1, " \n"[i + 1 == res.size()]);
  }
}
int main() {
  int kkt;
  scanf("%d", &kkt);
  while (kkt--) {
    solve();
  }
  return 0;
}
