Circular Xor Reversal

2000ms

262144K

Description:

You have an array $$$a_0, a_1, \ldots, a_{n-1}$$$ of length $$$n$$$. Initially, $$$a_i = 2^i$$$ for all $$$0 \le i \lt n$$$. Note that array $$$a$$$ is zero-indexed.

You want to reverse this array (that is, make $$$a_i$$$ equal to $$$2^{n-1-i}$$$ for all $$$0 \le i \lt n$$$). To do this, you can perform the following operation no more than $$$250\,000$$$ times:

Select an integer $$$i$$$ ($$$0 \le i \lt n$$$) and replace $$$a_i$$$ by $$$a_i \oplus a_{(i+1)\bmod n}$$$.

Here, $$$\oplus$$$ denotes the bitwise XOR operation.

Your task is to find any sequence of operations that will result in the array $$$a$$$ being reversed. It can be shown that under the given constraints, a solution always exists.

Input:

The first line contains a single integer $$$n$$$ ($$$2 \le n \le 400$$$) — the length of the array $$$a$$$.

Output:

On the first line print one integer $$$k$$$ ($$$0 \le k \le 250\,000$$$) — the number of operations performed.

On the second line print $$$k$$$ integers $$$i_1,i_2,\ldots,i_k$$$ ($$$0 \le i_j \lt n$$$). Here, $$$i_j$$$ should be the integer selected on the $$$j$$$-th operation.

Note that you don't need to minimize the number of operations.

Sample Input:

Sample Output:

3
1 0 1

Sample Input:

Sample Output:

9
1 0 1 0 2 1 0 1 0

Note:

In the notes, the elements on which the operations are performed are colored red.

In the first test case, array $$$a$$$ will change in the following way:

$$$[1,\color{red}{2}] \rightarrow [\color{red}{1},3] \rightarrow [2,\color{red}{3}] \rightarrow [2,1]$$$.

In the second test case, array $$$a$$$ will change in the following way:

$$$[1,\color{red}{2},4] \rightarrow [\color{red}{1},6,4] \rightarrow [7,\color{red}{6},4] \rightarrow [\color{red}{7},2,4] \rightarrow [5,2,\color{red}{4}] \rightarrow [5,\color{red}{2},1] \rightarrow [\color{red}{5},3,1] \rightarrow [6,\color{red}{3},1] \rightarrow [\color{red}{6},2,1] \rightarrow [4,2,1]$$$.

Informação

Provedor Codeforces

Código CF1748F