I have just started practicing with recursion I have this very simple practice program problem.

There are bunnies standing in a line, numbered 1,2,3… The odd bunnies (1,2,3..) have normal 2 ears.

The even bunnies (2,4,6…) have 3 ears, because they each have a raised foot. Recursively return the number of ears in the bunny line.

I have the solution. However, I am a bit confused on certain things. For one, it is my understanding that each even numbered rabbit has 3 feet. So bunnyEars2(2), should produce 6 instead of 5?

Also, I notice if I remove certain intricacies like ‘(bunnyEars2(bunnies)’ instead of adding in the ‘-1’ at the end. I get this duplicitous message “at bunnyEarsTwo.bunnyEars2(bunnyEarsTwo.java:13).

Any explanation and breakdown of this problem and recursion in general is very much appreciated. I am determined to learn, I just want to be pointed in the right direction!

public static int bunnyEars2(int bunnies){ if(bunnies==0) return 0; return (bunnies % 2 == 0) ? (3+bunnyEars2(bunnies-1)) : (2+bunnyEars2(bunnies-1)); }

## Advertisement

## Answer

I hope you know factorial by recursive. because this is very similar.

int factorial(int n){ if (n == 0) return 1; else return(n * factorial(n-1)); }

Here we are returning `n * n-1 * n-1-1 * n-1-1-1 and so on until it n-1…. is 0.

Likewise,

public static int bunnyEars2(int bunnies){ if(bunnies==0) return 0; if (bunnies % 2 == 0) return 3+bunnyEars2(bunnies-1); else return 2+bunnyEars2(bunnies-1); }

Here, follows same logic, but the differece is ,

when its even, it return `3 + bunnyEars2(bunnies-1)`

when its odd, it return `2 + bunnyEars2(bunnies-1)`

for example: `bunnyEars2(4)`

is `10`

here our bunnies value will be `4,3,2,1,0`

as 4 is even it returns `3+`

, 3 is odd it returns `2+`

, 2 returns `3+`

, 1 returns `2+`

and 0 returns `0`

3 + 2 + 3 + 2 + 0 = 10.

`bunnyEars2(2)`

will be `5`

, here bunnies value will be `2,1,0`

which returns `3 + 2 + 0 = 5`

Also removing `-1`

from `bunnyEars2(bunnies-1)`

will result in infinite recursion(stack overflow error). It’s like removing `-1`

from `n * factorial(n)`

, it won’t end.