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();
        int [] arr = new int[n];
        for (int i = 0; i <= n - 1; ++i) {

            if (i == 0) {
                arr[i] = 0;
            } else if (i == 1 | i == 2) {
                arr[i] = 1;
            } else {
                arr[i] = arr[i - 3] + 2 * arr[i - 2] + arr[i - 1];

            }
        }
        System.out.print(arr[n - 1]);

    }
}