题解 | 牛牛学数列6

import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);

        int n = in.nextInt();

        if (n == 1) {
            System.out.println(0);
        } else if (n == 2 || n == 3) {
            System.out.println(1);
        } else {
            int []arr = new int[n + 1];
            arr[0] = 0;
            arr[1] = 1;
            arr[2] = 1;
            for (int i = 3; i <n; i++) {

                arr[i] = arr[i - 3] + 2 * arr[i - 2] + arr[i - 1];
            }
            System.out.println(arr[n-1]);
        }
    }
}

简如单