1175. Prime Arrangements.md

题目

1175. Prime Arrangements

思路

4ms 65.51%

代码

class Solution {
public:
    const int m=1e9+7;
    bool ispri(int n){
        for(int i=2;i<=sqrt(n);i++)
            if(n%i==0)return false;
        return true;
    }
    long long factorial(long long n){
        if(n==0)return 1;
        return (n*factorial(n-1))%m;
    }
    int numPrimeArrangements(int n) {
        int pri=0;
        for(int i=2;i<=n;i++) 
            if(ispri(i))pri++;
        int fac=n-pri;
        int ans=(factorial(pri)*factorial(fac))%m;
        return (int)ans;
    }
};