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## Problem

Suppose you have n integers labeled 1 through n. A permutation of those n integers perm (1-indexed) is considered a beautiful arrangement if for every i (1 <= i <= n), either of the following is true:

• perm[i] is divisible by i.
• i is divisible by perm[i].

Given an integer n, return the number of the beautiful arrangements that you can construct.

Example 1:

Input: n = 2
Output: 2
Explanation:
The first beautiful arrangement is [1,2]:
- perm = 1 is divisible by i = 1
- perm = 2 is divisible by i = 2
The second beautiful arrangement is [2,1]:
- perm = 2 is divisible by i = 1
- i = 2 is divisible by perm = 1


Example 2:

Input: n = 1
Output: 1


Constraints:

• 1 <= n <= 15

## Code

class Solution {
int res = 0;

public int countArrangement(int n) {
helper(n, 1, new boolean[n + 1]);
return res;
}

private void helper(int n, int curr, boolean[] visited) {
if (curr > n) {
res++;
return;
}

for (int i = 1; i <= n; i++) {
if(visited[i]) continue;

if (i % curr == 0 || curr % i == 0) {
visited[i] = true;
helper(n, curr + 1, visited);
visited[i] = false;
}
}
}
}