526.cpp

// simple.cpp
class Solution {
  int count;

public:
  int countArrangement(int N) {
    vector<int> visited(N + 1, 0);
    recursion(visited, N, 1);
    return count;
  }
  void recursion(vector<int> &visited, int N, int cur) {
    if (cur > N) {
      ++count;
      return;
    }
    for (int i = 1; i <= N; ++i)
      if (visited[i] == 0 && (i % cur == 0 || cur % i == 0)) {
        visited[i] = 1;
        recursion(visited, N, cur + 1);
        visited[i] = 0;
      }
  }
};