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;
  int a[2005], ans[10005], n, le;
  int read() {
    char ch = getchar();
    int X = 0;
    bool fl = 0;
    while (ch < '0' || ch > '9') {
      if (ch == '-') fl = 1;
      ch = getchar();
    }
    while (ch >= '0' && ch <= '9') {
      X = (X << 1) + (X << 3) + ch - '0';
      ch = getchar();
    }
    if (fl) return ~(X - 1);
    return X;
  }
  int ck(int x) {
    for (int i = 1; i <= n; i++)
      if (a[i] == x) return i;
  }
  int T;
  int main() {
    T = read();
    for (; T; T--) {
      n = read();
      le = 0;
      bool fl = 0;
      for (int i = 1; i <= n; i++) a[i] = read();
      for (int i = 1; i <= n; i++)
        if (abs(a[i] - i) & 1) {
          puts("-1");
          fl = 1;
          break;
        }
      if (fl) {
        continue;
      }
      for (int i = 1; i <= n / 2; i++) {
        int p1 = ck(i * 2 - 1);
        reverse(a + 1, a + p1 + 1);
        ans[++le] = p1;
        int p2 = ck(i * 2);
        reverse(a + 1, a + p2);
        ans[++le] = p2 - 1;
        reverse(a + 1, a + p2 + 2);
        ans[++le] = p2 + 1;
        reverse(a + 1, a + 4);
        ans[++le] = 3;
        reverse(a + 1, a + n - i * 2 + 3);
        ans[++le] = n - i * 2 + 2;
      }
      reverse(a + 1, a + 1 + n);
      ans[++le] = n;
      cout << le << '\n';
      for (int i = 1; i <= le; i++) cout << ans[i] << ' ';
      puts("");
    }
    return 0;
  }
  