#include <bits/stdc++.h>
int main() {
  std::ios::sync_with_stdio(false);
  std::cin.tie(NULL);
  int T;
  std::cin >> T;
  while (T--) {
    int n;
    std::cin >> n;
    std::vector<int> a(n), cnt(500, 0), mem;
    for (int i = 0; i < n; i++) {
      std::cin >> a[i];
      --a[i];
      ++cnt[a[i]];
    }
    mem = a;
    for (int i = 1; i < 500; i++) {
      cnt[i] += cnt[i - 1];
    }
    std::vector<int> b = a;
    for (int i = 0; i < n; i++) b[i] = --cnt[a[i]];
    a = b;
    std::vector<int> answer;
    auto solve = [&]() {
      for (int k = 0; k < n - 2; k++) {
        int mn = 1e9, pos;
        for (int i = k; i < n; i++)
          if (a[i] < mn) {
            mn = a[i];
            pos = i;
          }
        for (int i = pos; i > k;) {
          if (i == k + 1) {
            answer.push_back(k);
            answer.push_back(k);
            --i;
            std::swap(a[i], a[i + 1]);
            std::swap(a[i], a[i + 2]);
            std::swap(a[i], a[i + 1]);
            std::swap(a[i], a[i + 2]);
            break;
          } else {
            answer.push_back(i - 2);
            i -= 2;
            std::swap(a[i], a[i + 1]);
            std::swap(a[i], a[i + 2]);
          }
        }
      }
      bool flag = true;
      for (int i = 1; i < n; i++)
        if (a[i] < a[i - 1]) {
          flag = false;
        }
      return flag;
    };
    if (solve()) {
      std::cout << answer.size() << '\n';
      for (auto i : answer) {
        std::cout << i + 1 << ' ';
      }
      std::cout << '\n';
    } else {
      answer.clear();
      cnt.assign(500, -1);
      a = mem;
      for (int i = 0; i < n; i++) {
        if (~cnt[a[i]]) {
          std::swap(b[cnt[a[i]]], b[i]);
          break;
        } else {
          cnt[a[i]] = i;
        }
      }
      a = b;
      if (solve()) {
        std::cout << answer.size() << '\n';
        for (auto i : answer) {
          std::cout << i + 1 << ' ';
        }
        std::cout << '\n';
      } else {
        std::cout << -1 << '\n';
      }
    }
  }
  return 0;
}
