小蓝与钥匙（错排）

https://www.lanqiao.cn/problems/2167/learning/?subject_code=2&group_code=5&match_num=13&match_flow=2&origin=cup

 

import java.util.Scanner;
// 1:无需package
// 2: 类名必须Main, 不可修改

public class 小蓝选钥匙 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        long a =14;
        long n1 = 28;
        long m = 14;
        System.out.println(C(n1,m)*D(a));

    }//全错排列 错位的14把
    static long D(long a){
      if(a==0||a==1){
        return 0;
      }
      else if(a==2){
        return 1;
      }
      else{
        return (a-1)*(D(a-2)+D(a-1));
      }
    }
    //组合C 14 28
    static long C(long n,long m){
      long res = 1L;
      for(int i = 0;i<m;i++){
       res = res*(n-i)/(i+1);
      }
      return res;
    }
}