Cyclic Shifts Sorting

2000ms

262144K

Description:

You are given an array $$$a$$$ consisting of $$$n$$$ integers.

In one move, you can choose some index $$$i$$$ ($$$1 \le i \le n - 2$$$) and shift the segment $$$[a_i, a_{i + 1}, a_{i + 2}]$$$ cyclically to the right (i.e. replace the segment $$$[a_i, a_{i + 1}, a_{i + 2}]$$$ with $$$[a_{i + 2}, a_i, a_{i + 1}]$$$).

Your task is to sort the initial array by no more than $$$n^2$$$ such operations or say that it is impossible to do that.

You have to answer $$$t$$$ independent test cases.

Input:

The first line of the input contains one integer $$$t$$$ ($$$1 \le t \le 100$$$) — the number of test cases. Then $$$t$$$ test cases follow.

The first line of the test case contains one integer $$$n$$$ ($$$3 \le n \le 500$$$) — the length of $$$a$$$. The second line of the test case contains $$$n$$$ integers $$$a_1, a_2, \dots, a_n$$$ ($$$1 \le a_i \le 500$$$), where $$$a_i$$$ is the $$$i$$$-th element $$$a$$$.

It is guaranteed that the sum of $$$n$$$ does not exceed $$$500$$$.

Output:

For each test case, print the answer: -1 on the only line if it is impossible to sort the given array using operations described in the problem statement, or the number of operations $$$ans$$$ on the first line and $$$ans$$$ integers $$$idx_1, idx_2, \dots, idx_{ans}$$$ ($$$1 \le idx_i \le n - 2$$$), where $$$idx_i$$$ is the index of left border of the segment for the $$$i$$$-th operation. You should print indices in order of performing operations.

Sample Input:

5
5
1 2 3 4 5
5
5 4 3 2 1
8
8 4 5 2 3 6 7 3
7
5 2 1 6 4 7 3
6
1 2 3 3 6 4

Sample Output:

0

6
3 1 3 2 2 3 
13
2 1 1 6 4 2 4 3 3 4 4 6 6 
-1
4
3 3 4 4

Informação

Provedor Codeforces

Código CF1374F