力扣：1175. 质数排列

 题都看不懂，直接CV官方答案

 
 
/**
 * @author xnl
 * @Description:
 * @date: 2022/6/30   21:46
 */
public class Solution {
    public static void main(String[] args) {
        Solution solution = new Solution();
 
    }
 
    static final int MOD = 1000000007;
 
    public int numPrimeArrangements(int n) {
        int numPrime = 0;
        for (int i = 1; i <= n; i++){
            if (isPrime(i)){
                numPrime++;
            }
        }
        return (int)(factorial(numPrime) * factorial(n - numPrime) % MOD);
    }
 
    private boolean isPrime(int n){
        if (n == 1){
            return false;
        }
 
        for (int i = 2; i * i <= n; i++){
            if (n % i == 0){
                return false;
            }
        }
        return true;
    }
 
    private long factorial(int n ){
        long res = 1;
        for (int i = 1; i <= n; i++){
            res *= i;
            res %= MOD;
        }
        return res;
    }
}