Double Sort II

有两个 $1..n$ 的排列 $a,b$。 你可以进行若干次操作，每次操作流程如下： * 选择一个整数 $i∈[1,n]$。 * 找出两个整数 $x,y$，使得 $a_x=b_y=i$。 * 交换 $a_x$ 和 $a_i$，以及 $b_y$ 和 $b_i$。 问把 $a$ 和 $b$ 从小到大排序的最小操作次数

You are given two permutations $ a $ and $ b $ , both of size $ n $ . A permutation of size $ n $ is an array of $ n $ elements, where each integer from $ 1 $ to $ n $ appears exactly once. The elements in each permutation are indexed from $ 1 $ to $ n $ . You can perform the following operation any number of times: - choose an integer $ i $ from $ 1 $ to $ n $ ; - let $ x $ be the integer such that $ a_x = i $ . Swap $ a_i $ with $ a_x $ ; - let $ y $ be the integer such that $ b_y = i $ . Swap $ b_i $ with $ b_y $ . Your goal is to make both permutations sorted in ascending order (i. e. the conditions $ a_1 < a_2 < \dots < a_n $ and $ b_1 < b_2 < \dots < b_n $ must be satisfied) using minimum number of operations. Note that both permutations must be sorted after you perform the sequence of operations you have chosen.

The first line contains one integer $ n $ ( $ 2 \le n \le 3000 $ ). The second line contains $ n $ integers $ a_1, a_2, \dots, a_n $ ( $ 1 \le a_i \le n $ ; all $ a_i $ are distinct). The third line contains $ n $ integers $ b_1, b_2, \dots, b_n $ ( $ 1 \le b_i \le n $ ; all $ b_i $ are distinct).

First, print one integer $ k $ ( $ 0 \le k \le 2n $ ) — the minimum number of operations required to sort both permutations. Note that it can be shown that $ 2n $ operations are always enough. Then, print $ k $ integers $ op_1, op_2, \dots, op_k $ ( $ 1 \le op_j \le n $ ), where $ op_j $ is the value of $ i $ you choose during the $ j $ -th operation. If there are multiple answers, print any of them.

5
1 3 2 4 5
2 1 3 4 5

1
2

2
1 2
1 2

0

4
1 3 4 2
4 3 2 1

2
3 4