[LeetCode] 526. Beautiful Arrangement

void caHelp(int &res,vector<int> &v,int N,int cnt){if(cnt==N+1){++res;return;}for(int i=1;i<=N;++i){if(v[i]==0&&(i%cnt==0||cnt%i==0)){v[i]=1;caHelp(res,v,N,cnt+1);v[i]=0;}}}int countArrangement(int N){int res=0;vector<int> v(N+1,0);caHelp(res,v,N,1);return res;}