#include <bits/stdc++.h>
using namespace std;
inline long long read() {
  long long x = 0, w = 1;
  char c = getchar();
  while (c < '0' || c > '9') {
    if (c == '-') w = -1;
    c = getchar();
  }
  while (c <= '9' && c >= '0') {
    x = (x << 1) + (x << 3) + c - '0';
    c = getchar();
  }
  return w == 1 ? x : -x;
}
const int N = 5e2 + 10;
int n;
int a[N], vis[N];
int main() {
  int _ = read();
  while (_--) {
    n = read();
    for (int i = 1; i <= n; i++) a[i] = read();
    int base = 1;
    vector<int> ans;
    for (int k = 1; k < n - 1; ++k) {
      int mi = INT_MAX, id = 0;
      for (int i = base; i <= n; ++i) {
        if (a[i] < mi) mi = a[i], id = i;
      }
      while (id >= base + 2) {
        ans.push_back(id - 2);
        int tmp = a[id];
        a[id] = a[id - 1];
        a[id - 1] = a[id - 2];
        a[id - 2] = tmp;
        id = id - 2;
      }
      if (id == base + 1) {
        ans.push_back(base);
        ans.push_back(base);
        int tmp = a[id];
        a[id] = a[id + 1];
        a[id + 1] = a[base];
        a[base] = tmp;
      }
      base++;
    }
    int flag = 1;
    for (int i = 1; i + 1 <= n; ++i)
      if (a[i + 1] < a[i]) flag = 0;
    if (flag) {
      printf("%d\n", ans.size());
      for (int v : ans) printf("%d ", v);
      puts("");
    } else {
      int f = 0, mx = 0;
      for (int i = 1; i <= n; i++) mx = max(mx, a[i]);
      for (int i = 0; i <= mx; i++) vis[i] = 0;
      for (int i = 1; i <= n; i++) vis[a[i]]++;
      for (int i = 1; i <= n; i++)
        if (vis[a[i]] >= 2) f = 1;
      if (f) {
        int id = n;
        while (id - 1 >= 1 && a[id] < a[id - 1]) {
          ans.push_back(id - 2);
          int tmp = a[id];
          a[id] = a[id - 1];
          a[id - 1] = a[id - 2];
          a[id - 2] = tmp;
          id--;
        }
        printf("%d\n", ans.size());
        for (int v : ans) printf("%d ", v);
        puts("");
      } else
        puts("-1");
    }
  }
}
