#include <bits/stdc++.h>
using namespace std;
const int N = 200010;
int T, n, mk, a[N];
vector<int> res;
void flip(int x) {
  int t = a[x + 2];
  a[x + 2] = a[x + 1];
  a[x + 1] = a[x];
  a[x] = t;
}
void solve(int x, int y) {
  if (a[x] == a[x + 2]) {
    flip(x);
    flip(x);
    res.push_back(x);
    res.push_back(x);
    return;
  }
  if (y >= n - 1) {
    mk = 0;
    return;
  }
  if (a[x + 2] == a[y + 2]) {
    flip(y);
    flip(x);
    res.push_back(y);
    res.push_back(x);
    return;
  }
  solve(x + 1, y + 1);
  flip(x);
  res.push_back(x);
}
int main() {
  scanf("%d", &T);
  while (T--) {
    res.clear();
    scanf("%d", &n);
    for (int i = 1; i <= n; i++) scanf("%d", &a[i]);
    for (int i = n; i >= 3; i--) {
      int pos = 0, imax = 0;
      for (int k = 1; k <= i; k++) {
        if (a[k] > imax) {
          imax = a[k];
          pos = k;
        }
      }
      if (pos == i) continue;
      for (int k = 0; k < i - pos - 1; k++) {
        res.push_back(pos + k);
        flip(pos + k);
      }
      flip(i - 2);
      res.push_back(i - 2);
    }
    if (a[1] > a[2]) {
      mk = 1;
      solve(1, 2);
      if (0 == mk) {
        printf("-1\n");
        continue;
      }
    }
    printf("%d\n", res.size());
    for (int i = 0; i < res.size(); i++) {
      printf("%d", res[i]);
      printf(i == res.size() - 1 ? "\n" : " ");
    }
    if (0 == res.size()) printf("\n");
  }
  return 0;
}
