题目：

题解：

class Solution {
public:int countArrangement(int n) {vector<int> f(1 << n);f[0] = 1;for (int mask = 1; mask < (1 << n); mask++) {int num = __builtin_popcount(mask);for (int i = 0; i < n; i++) {if (mask & (1 << i) && (num % (i + 1) == 0 || (i + 1) % num == 0)) {f[mask] += f[mask ^ (1 << i)];}}}return f[(1 << n) - 1];}
};