题目：

题解：

class Solution {public int countArrangement(int n) {int[] f = new int[1 << n];f[0] = 1;for (int mask = 1; mask < (1 << n); mask++) {int num = Integer.bitCount(mask);for (int i = 0; i < n; i++) {if ((mask & (1 << i)) != 0 && ((num % (i + 1)) == 0 || (i + 1) % num == 0)) {f[mask] += f[mask ^ (1 << i)];}}}return f[(1 << n) - 1];}
}