题解 | 牛牛学数列6

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int result = Array(n);
        System.out.print(result);
    }
    public static int Array(int num){
        if(num == 1){
            return 0;
        }
        if(num == 2 || num == 3){
            return 1;
        }
        else{
            return Array(num-3) + 2*Array(num-2) + Array(num-1);//主要函数调用
        }
    }
}