Leetcode-5173 Prime Arrangements(质数排列)

#define _for(i,a,b) for(int i = (a);i < b;i ++)
#define _rep(i,a,b) for(int i = (a);i > b;i --)

class Solution
{
    public:
        bool is_prime(int n)
        {
            for(int i = 2; i * i <= n; i ++)
                if(n%i==0) return false;
            return n != 1;
        }
        long long go(int k)
        {
            long long rnt = 1;
            _for(i,1,k+1)
            {
                rnt = i*rnt;
                rnt %= 1000000007;
            }
            return (int)rnt;
        }
        int numPrimeArrangements(int n)
        {
            int k = 0;
            _for(i,1,n+1)
            if(is_prime(i))
                k ++;
            return (int)((go(k)*go(n-k))%1000000007);
        }
};