CF1681C 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.