递归练习

Question

所以我遇到了下面的问题:我们有兔子排成一列，编号为1，2，...奇数兔(1，3，..)偶数兔(2，4，..)我们说有3只耳朵，因为它们每只都有一只抬起的脚。递归返回bunny行1，2，...中的"ears“数

这是我的源代码。我使用的是Java

import java.util.Scanner;

public class BunnyEars
{
    public static int CountEars(int i, int e)
    {
        if(i == 0)
        {
            return e;
        }
        else if(i > 0)
        {
            if(i%2==0)
            {
                e = e + 2;
                i = i - 1;
                CountEars(i,e);
            }
            else
            {
                e = e + 3;
                i = i - 1;
                CountEars(i,e);
            }       
        }
        return e;
    }

public static void main(String []args)
{
    Scanner scan = new Scanner(System.in);

    int b;
    int result;

    System.out.println("Bunny Ears, even has 2 ears, odd has 3 ears");
    System.out.println("Please enter a value: ");
    b = scan.nextInt();

    result = CountEars(b,0);

    System.out.println("Number of ears are: " + result);
}

如果我输入5，输出应该是12，但是输出是3。

enter code here

if(i%2==0)
        {
            e = e + 2;
            i = i - 1;
            CountEars(i,e);
        }
        else
        {
            e = e + 3;
            i = i - 1;
            CountEars(i,e);
        }   

没有执行。我似乎找不到我的错误。有没有人？

Answer 1

在您的递归方法中，您不会合计来自行中其他bunnies的返回值。而且，您只需要一个参数--正在考虑的是哪只兔子。

/*
 * Return the total number of ears in a line of length n
 */
public static int countEars(int n) {
   if (n < 1) {
      return 0;   // base case: no bunnies, no ears
   }
   // Below we make the "recursive leap of faith": if this
   // function works, we can get the answer for a line of n-1
   // bunnies and add the current bunny's ears to it to yield
   // the correct answer for the current value of n.
   // Note that the argument to the recursive call must
   // converge towards the base case for this to work.
   if (n % 2 == 1) {
      return 2 + countEars(n-1);
   }
   return 3 + countEars(n-1);
}

使用result = countEars(5);调用此函数。

请注意，我已经重命名了您的方法，使其也遵循Java约定。

Answer 2

试试这段代码

import java.util.Scanner;

public class BunnyEars {

static int e=0;
public static int CountEars(int i) {
    if (i == 0) {
        return e;
    } else if (i > 0) {
        if (i % 2 == 0) {
            e = e + 2;
            //i = i - 1;
            CountEars(i-1);
        } else {
            e = e + 3;
            //i = i - 1;
            CountEars(i-1);
        }
    }
    return e;
}

public static void main(String[] args) {
    Scanner scan = new Scanner(System.in);

    int b;
    int result;

    System.out.println("Bunny Ears, even has 2 ears, odd has 3 ears");
    System.out.println("Please enter a value: ");
    b = scan.nextInt();

    result = CountEars(b);

    System.out.println("Number of ears are: " + result);
}
}