#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
using namespace std;
using ll = long long;
using ull = unsigned long long;
using ld = long double;
template <typename T>
using mat = vector<vector<T>>;
template <int mod>
struct modint {
  int x;
  modint() : x(0) {}
  modint(int64_t y) : x(y >= 0 ? y % mod : (mod - (-y) % mod) % mod) {}
  modint &operator+=(const modint &p) {
    if ((x += p.x) >= mod) x -= mod;
    return *this;
  }
  modint &operator-=(const modint &p) {
    if ((x += mod - p.x) >= mod) x -= mod;
    return *this;
  }
  modint &operator*=(const modint &p) {
    x = (int)(1LL * x * p.x % mod);
    return *this;
  }
  modint &operator/=(const modint &p) {
    *this *= p.inverse();
    return *this;
  }
  modint operator-() const { return modint(-x); }
  modint operator+(const modint &p) const { return modint(*this) += p; }
  modint operator-(const modint &p) const { return modint(*this) -= p; }
  modint operator*(const modint &p) const { return modint(*this) *= p; }
  modint operator/(const modint &p) const { return modint(*this) /= p; }
  bool operator==(const modint &p) const { return x == p.x; }
  bool operator!=(const modint &p) const { return x != p.x; }
  modint inverse() const {
    int a = x, b = mod, u = 1, v = 0, t;
    while (b > 0) {
      t = a / b;
      swap(a -= t * b, b);
      swap(u -= t * v, v);
    }
    return modint(u);
  }
  modint pow(int64_t n) const {
    modint ret(1), mul(x);
    while (n > 0) {
      if (n & 1) ret *= mul;
      mul *= mul;
      n >>= 1;
    }
    return ret;
  }
  friend ostream &operator<<(ostream &os, const modint &p) { return os << p.x; }
  friend istream &operator>>(istream &is, modint &a) {
    int64_t t;
    is >> t;
    a = modint<mod>(t);
    return (is);
  }
  static int get_mod() { return mod; }
};
ll gcd(ll a, ll b) { return b ? gcd(b, a % b) : a; }
ll lcm(ll a, ll b) { return a / gcd(a, b) * b; }
template <class T>
bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T>
bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return 1;
  }
  return 0;
}
template <typename T>
T mypow(T x, ll n) {
  T ret = 1;
  while (n > 0) {
    if (n & 1) (ret *= x);
    (x *= x);
    n >>= 1;
  }
  return ret;
}
ll modpow(ll x, ll n, const ll mod) {
  ll ret = 1;
  while (n > 0) {
    if (n & 1) (ret *= x);
    (x *= x);
    n >>= 1;
    x %= mod;
    ret %= mod;
  }
  return ret;
}
uint64_t my_rand(void) {
  static uint64_t x = 88172645463325252ULL;
  x = x ^ (x << 13);
  x = x ^ (x >> 7);
  return x = x ^ (x << 17);
}
ll popcnt(ull x) { return __builtin_popcountll(x); }
template <typename T>
struct edge {
  int src, to;
  T cost;
  edge(int to, T cost) : src(-1), to(to), cost(cost) {}
  edge(int src, int to, T cost) : src(src), to(to), cost(cost) {}
  edge &operator=(const int &x) {
    to = x;
    return *this;
  }
  bool operator<(const edge<T> &r) const { return cost < r.cost; }
  operator int() const { return to; }
};
template <typename T>
using Edges = vector<edge<T>>;
template <typename T>
using WeightedGraph = vector<Edges<T>>;
using UnWeightedGraph = vector<vector<int>>;
struct Timer {
  clock_t start_time;
  void start() { start_time = clock(); }
  int lap() { return (clock() - start_time) * 1000 / CLOCKS_PER_SEC; }
};
const long double eps = 0.000001;
const long double PI = 3.141592653589793;
template <typename T>
struct BIT {
  vector<T> data;
  BIT(int sz) { data.assign(++sz, 0); }
  T sum(int k) {
    T ret = 0;
    for (; k > 0; k -= k & -k) ret += data[k];
    return (ret);
  }
  void add(int k, T x) {
    for (++k; k < data.size(); k += k & -k) data[k] += x;
  }
  int search(long long k) {
    ++k;
    int res = 0;
    int N = 1;
    while (N < (int)data.size()) N *= 2;
    for (int i = N / 2; i > 0; i /= 2) {
      if (res + i < (int)data.size() && data[res + i] < k) {
        k = k - data[res + i];
        res = res + i;
      }
    }
    return res;
  }
  void show() {
    for (ll i = (0), max_i = (((ll)(data).size()) - 1); i < max_i; i++)
      cout << sum(i + 1) - sum(i) << ' ';
    cout << '\n';
  }
};
ll inversion_number(vector<int> &x, int n) {
  BIT<int> bit(n);
  ll res = 0;
  for (int &y : x) {
    res += bit.sum(n - 1 - y);
    bit.add(n - 1 - y, 1);
  }
  return res;
}
void move(vector<int> &x, vector<int> &y, int i) {
  assert(x.size() - 2 > i);
  int a = x[i], b = x[i + 1], c = x[i + 2];
  swap(y[a], y[b]);
  swap(y[c], y[b]);
  swap(x[i + 2], x[i + 1]);
  swap(x[i], x[i + 1]);
}
void solve() {
  int n;
  cin >> n;
  vector<int> a(n);
  vector<pair<int, int>> inv(n);
  for (ll i = (0), max_i = (n); i < max_i; i++)
    cin >> a[i], inv[i] = make_pair(a[i], i);
  sort((inv).begin(), (inv).end());
  vector<int> id(n);
  for (ll i = (0), max_i = (n); i < max_i; i++) id[i] = inv[i].second;
  int num = inversion_number(id, n);
  if (num % 2 == 1) {
    bool flag = false;
    for (ll i = (0), max_i = (n - 1); i < max_i; i++) {
      if (inv[i].first == inv[i + 1].first) {
        swap(inv[i].second, inv[i + 1].second);
        swap(id[i], id[i + 1]);
        flag = true;
        break;
      }
    }
    if (not flag) {
      cout << -1 << '\n';
      return;
    }
  }
  vector<int> now(n), now_inv(n);
  iota((now).begin(), (now).end(), 0);
  iota((now_inv).begin(), (now_inv).end(), 0);
  vector<int> ans;
  for (ll i = (0), max_i = (n); i < max_i; i++) {
    int a = id[i];
    while (now_inv[a] != i) {
      if (now_inv[a] == n - 1) {
        ans.push_back(now_inv[a] - 1);
        move(now, now_inv, now_inv[a] - 2);
        continue;
      }
      int tmp = now_inv[a] - 1;
      ans.push_back(tmp + 1);
      ans.push_back(tmp + 1);
      move(now, now_inv, tmp);
      move(now, now_inv, tmp);
    }
  }
  cout << ans.size() << '\n';
  for (ll i = (0), max_i = (ans.size()); i < max_i; i++) cout << ans[i] << ' ';
  cout << '\n';
}
int main() {
  cin.tie(0);
  ios::sync_with_stdio(0);
  cout << setprecision(20);
  int t;
  cin >> t;
  for (ll _ = (0), max_i = (t); _ < max_i; _++) {
    solve();
  }
}
