A15140. Double Sort

You are given two arrays $a$ and $b$ , both consisting of $n$ integers.

In one move, you can choose two indices $i$ and $j$ ( $1 \le i, j \le n$ ; $i \neq j$ ) and swap $a_i$ with $a_j$ and $b_i$ with $b_j$ . You have to perform the swap in both arrays.

You are allowed to perform at most $10^4$ moves (possibly, zero). Can you make both arrays sorted in a non-decreasing order at the end? If you can, print any sequence of moves that makes both arrays sorted.

The first line contains a single integer $t$ ( $1 \le t \le 100$ ) — the number of testcases.

The first line of each testcase contains a single integer $n$ ( $2 \le n \le 100$ ) — the number of elements in both arrays.

The second line contains $n$ integers $a_1, a_2, \dots, a_n$ ( $1 \le a_i \le n$ ) — the first array.

The third line contains $n$ integers $b_1, b_2, \dots, b_n$ ( $1 \le b_i \le n$ ) — the second array.

For each testcase, print the answer. If it's impossible to make both arrays sorted in a non-decreasing order in at most $10^4$ moves, print -1. Otherwise, first, print the number of moves $k$ $(0 \le k \le 10^4)$ . Then print $i$ and $j$ for each move $(1 \le i, j \le n$ ; $i \neq j)$ .

If there are multiple answers, then print any of them. You don't have to minimize the number of moves.