#include <bits/stdc++.h>
using namespace std;
const int MAXN = 505;
int arr[MAXN];
int arr_copy[MAXN];
void rotate(int ind) {
  int num1 = arr[ind], num2 = arr[ind + 1], num3 = arr[ind + 2];
  arr[ind] = num3;
  arr[ind + 1] = num1;
  arr[ind + 2] = num2;
}
void swap_back(int ind, int distance, vector<int>& actions) {
  if (distance == 0) return;
  if (distance == 1) {
    actions.push_back(ind - 1);
    actions.push_back(ind - 1);
    rotate(ind - 1);
    rotate(ind - 1);
    return;
  }
  actions.push_back(ind - 2);
  rotate(ind - 2);
  swap_back(ind - 2, distance - 2, actions);
}
void swap_back2(int ind, int distance, vector<int>& actions) {
  if (distance <= 1) return;
  actions.push_back(ind - 2);
  rotate(ind - 2);
  swap_back2(ind - 2, distance - 2, actions);
}
int main() {
  ios_base::sync_with_stdio(0);
  int t;
  cin >> t;
  for (int test = 1; test <= t; test++) {
    int n;
    cin >> n;
    for (int i = 1; i <= n; i++) {
      cin >> arr[i];
      arr_copy[i] = arr[i];
    }
    vector<int> actions;
    for (int i = 1; i <= n - 2; i++) {
      int min_ind = -1, min_val = 1e9;
      for (int j = i; j <= n; j++) {
        if (arr[j] < min_val) min_val = arr[j], min_ind = j;
      }
      swap_back(min_ind, min_ind - i, actions);
    }
    if (arr[n - 1] <= arr[n]) {
      cout << actions.size() << '\n';
      for (int i : actions) cout << i << ' ';
      cout << '\n';
      continue;
    }
    for (int i = 1; i <= n; i++) arr[i] = arr_copy[i] * 501;
    int done = 0;
    for (int i = 1; i <= n; i++) {
      int num = arr[i] + 1;
      for (int j = i + 1; j <= n; j++) {
        if (arr[i] == arr[j]) {
          arr[j] = num;
          num++;
        }
      }
    }
    actions.clear();
    for (int i = 1; i <= n - 2; i++) {
      int min_ind = -1, min_val = 1e9;
      for (int j = i; j <= n; j++) {
        if (arr[j] < min_val) min_val = arr[j], min_ind = j;
      }
      swap_back(min_ind, min_ind - i, actions);
    }
    if (arr[n - 1] / 501 <= arr[n] / 501) {
      cout << actions.size() << '\n';
      for (int i : actions) cout << i << ' ';
      cout << '\n';
      continue;
    }
    for (int i = 1; i <= n; i++) arr[i] = arr_copy[i] * 501;
    done = 0;
    for (int i = 1; i <= n; i++) {
      int num = arr[i] + 1;
      for (int j = i + 1; j <= n; j++) {
        if (arr[i] == arr[j]) {
          arr[j] = num;
          num++;
        }
      }
    }
    for (int i = 1; i <= n; i++) {
      for (int j = i + 1; j <= n; j++) {
        if (arr[j] == arr[i] + 1) {
          swap(arr[i], arr[j]);
          done = 1;
          break;
        }
      }
      if (done) break;
    }
    actions.clear();
    for (int i = 1; i <= n - 2; i++) {
      int min_ind = -1, min_val = 1e9;
      for (int j = i; j <= n; j++) {
        if (arr[j] < min_val) min_val = arr[j], min_ind = j;
      }
      swap_back(min_ind, min_ind - i, actions);
    }
    if (arr[n - 1] / 501 <= arr[n] / 501) {
      cout << actions.size() << '\n';
      for (int i : actions) cout << i << ' ';
      cout << '\n';
      continue;
    } else
      cout << -1 << '\n';
  }
  return 0;
}
