Java 2.3题代码怎么写呢什么规律

Question

Answer 1

就是递归函数的简单应用

package com.csdn;

public class Solution {

    public static void main(String[] args) {
        System.out.println(func2(10));
        System.out.println(func3(10));

    }

    public static int func2(int n) {
        if (n == 0)
            return 1;
        if (n == 1)
            return 4;
        return 2 * func2(n - 1) + func2(n - 2);
    }

    public static int func3(int n) {
        if (n == 20)
            return 1;
        if (n == 21)
            return 4;
        return func3(n + 2) - 2 * func3(n + 1);
    }

}