description: You have a permutation: an array a = [a_1, a_2, …, a_n] of distinct integers from 1 to n. The length of the permutation n is odd.
  
  You need to sort the permutation in increasing order.
  
  In one step, you can choose any prefix of the permutation with an odd length and reverse it. Formally, if a = [a_1, a_2, …, a_n], you can choose any odd integer p between 1 and n, inclusive, and set a to [a_p, a_{p-1}, …, a_1, a_{p+1}, a_{p+2}, …, a_n].
  
  Find a way to sort a using no more than 5n/2 reversals of the above kind, or determine that such a way doesn't exist. The number of reversals doesn't have to be minimized.
  
  Input
  
  Each test contains multiple test cases. The first line contains the number of test cases t (1 ≤ t ≤ 100). Description of the test cases follows.
  
  The first line of each test case contains a single integer n (3 ≤ n ≤ 2021; n is odd) — the length of the permutation.
  
  The second line contains n distinct integers a_1, a_2, …, a_n (1 ≤ a_i ≤ n) — the permutation itself. 
  
  It is guaranteed that the sum of n over all test cases does not exceed 2021.
  
  Output
  
  For each test case, if it's impossible to sort the given permutation in at most 5n/2 reversals, print a single integer -1.
  
  Otherwise, print an integer m (0 ≤ m ≤ 5n/2), denoting the number of reversals in your sequence of steps, followed by m integers p_i (1 ≤ p_i ≤ n; p_i is odd), denoting the lengths of the prefixes of a to be reversed, in chronological order.
  
  Note that m doesn't have to be minimized. If there are multiple answers, print any.
  
  Example
  
  Input
  
  
  3
  3
  1 2 3
  5
  3 4 5 2 1
  3
  2 1 3
  
  
  Output
  
  
  4
  3 3 3 3
  2
  3 5
  -1
  
  Note
  
  In the first test case, the permutation is already sorted. Any even number of reversals of the length 3 prefix doesn't change that fact.
  
  In the second test case, after reversing the prefix of length 3 the permutation will change to [5, 4, 3, 2, 1], and then after reversing the prefix of length 5 the permutation will change to [1, 2, 3, 4, 5].
  
  In the third test case, it's impossible to sort the permutation.
solution: #include <bits/stdc++.h>
  using namespace std;
  const int N = 2027;
  template <typename T>
  void read(T &x) {
    bool neg = false;
    unsigned char c = getchar();
    for (; (c ^ 48) > 9; c = getchar())
      if (c == '-') neg = true;
    for (x = 0; (c ^ 48) < 10; c = getchar()) x = (x << 3) + (x << 1) + (c ^ 48);
    if (neg) x = -x;
  }
  int t, n, a[N], m, ans[5 * N];
  bool check() {
    for (int i = 0, i_end = n; i < i_end; ++i)
      if ((i & 1) != (a[i] & 1)) return false;
    return true;
  }
  void op(int len) {
    for (int i = 0, i_end = len / 2; i < i_end; ++i)
      a[i] ^= a[len - 1 - i] ^= a[i] ^= a[len - 1 - i];
    ans[m++] = len;
  }
  void solve(int n) {
    int apos, bpos;
    if (n == 1) return;
    for (int i = 0, i_end = n; i < i_end; ++i)
      if (a[i] == n - 1) bpos = i;
    op(++bpos);
    for (int i = 0, i_end = n; i < i_end; ++i)
      if (a[i] == n - 2) apos = i;
    op(apos);
    op(apos + 2);
    op(3);
    op(n);
    solve(n - 2);
  }
  int main() {
    read(t);
    while (t--) {
      read(n);
      for (int i = 0, i_end = n; i < i_end; ++i) read(a[i]), --a[i];
      if (check()) {
        m = 0;
        solve(n);
        printf("%d\n", m);
        for (int i = 0, i_end = m; i < i_end; ++i) printf("%d ", ans[i]);
        puts("");
      } else
        puts("-1");
    }
    return 0;
  }
  