#include <bits/stdc++.h>
using namespace std;
const int N = 502;
int t, n, a[N], b[N];
vector<int> ans;
void op(int i) {
  ans.push_back(i);
  int tmp = a[i + 2];
  a[i + 2] = a[i + 1], a[i + 1] = a[i];
  a[i] = tmp;
}
void solve(int l, int r) {
  int mn = 1000000;
  for (int i = l; i <= r; i++) mn = min(mn, a[i]);
  if (a[l] == mn) return;
  int pos = 0;
  for (int i = l; i <= r; i++)
    if (a[i] == mn) pos = i;
  if ((pos - l) % 2 == 1) {
    if (pos == r) op(pos - 2), pos = pos - 2;
    op(pos - 1);
    pos++;
  }
  for (int i = pos - 2; i >= l; i -= 2) {
    op(i);
  }
}
int main() {
  scanf("%d", &t);
  while (t--) {
    scanf("%d", &n);
    ans.clear();
    for (int i = 1; i <= n; i++) scanf("%d", &a[i]), b[i] = a[i], a[i] *= 1000;
    int inv = 0;
    for (int i = 1; i <= n; i++)
      for (int j = i + 1; j <= n; j++)
        if (a[i] > a[j]) inv++;
    for (int i = 1; i <= n; i++) {
      int cnt = 0;
      for (int j = 1; j < i; j++)
        if (b[i] == b[j]) a[i]++;
    }
    if (inv % 2) {
      bool fg = 0;
      for (int i = 1; i <= n; i++) {
        if (fg) break;
        for (int j = i + 1; j <= n; j++) {
          if (fg) break;
          if (b[i] == b[j]) {
            swap(a[i], a[j]);
            fg = 1;
          }
        }
      }
      if (!fg) {
        printf("-1\n");
        continue;
      }
    }
    for (int i = 1; i <= n; i++) {
      solve(i, n);
    }
    bool fg = 1;
    for (int i = 1; i < n; i++)
      if (a[i] > a[i + 1]) fg = 0;
    if (!fg) {
      printf("-1\n");
      continue;
    }
    printf("%d\n", ans.size());
    for (auto x : ans) printf("%d ", x);
    printf("\n");
    for (int i = 1; i < n; i++) assert(a[i] <= a[i + 1]);
  }
}
