Comp Sci Find the previous Fibonacci number: java

[cgrumiea]

Homework Statement

The first several numbers in the "Fibonacci Sequence" are 0, 1, 1, 2, 3, 5, 8, 13, 21, ... Each number is formed by summing the two previous numbers. Define a method named prevFib that takes a non-zero Fibonacci number and returns the Fibonacci number that comes immediately before it in the sequence.

prevFib(21) ==> 13

Hint: use a recursive helper method.

Homework Equations

The Attempt at a Solution

I'm brand new at java and hardly understand the recursion within it. I know scheme, but this is a different ball game. My main question is what I should do for the recursive helper. Or how that will help when finding the previous Fib number. Any help would be appreciated.

 

[Hurkyl]

Forget java for a moment! Suppose you were asked to find the Fibonacci number that comes before 1346269, by any means at all. How would you go about doing it?

 

[cgrumiea]

Forgive me if I sound like a total idiot here. I'm just genuinely lost.
I guess one way would be to start from scratch and add everything up until you get there, then look back one. That just seems like the most concrete way to me, since I can't seem to come up with a formula or anything.

 

[Hurkyl]

I guess one way would be to start from scratch and add everything up until you get there, then look back one.

That sounds like a perfectly reasonable algorithm. Now code it up in Java.