From: Todd Benson <caduceass@...>
Date: 2009-07-13T07:16:43+09:00
Subject: Re: Fibonacci numbers - newbie question.

On Sun, Jul 12, 2009 at 12:15 PM, jzakiya<jzakiya@mail.com> wrote:
> On Jul 12, 5:40 am, Stefano Crocco <stefano.cro...@alice.it> wrote:
>> On Sunday 12 July 2009, salai wrote:
>>
>>
>>
>> > |Dear All,
>> > |
>> > |I have two Fibonacci method, and I got different result.
>> > |
>> > |What wrong in my code.?
>> > |
>> > |def fib(n)
>> > |  if n < 2
>> > |          1
>> > |  else
>> > |          fib(n-2) + fib(n-1)
>> > |  end
>> > |end
>> > |
>> > |puts fib(10) # ---> 89
>> > |
>> > |
>> > |def fib1(x)
>> > |  return x if x < 2
>> > |  return fib1(x- 1) + fib1(x - 2)
>> > |end
>> > |
>> > |
>> > |
>> > |puts fib1(10) # --> 55
>> > |
>> > |
>> > |regards,
>> > |salai.
>>
>> In the first case, if the number is less than 2, you always return 1. In the
>> second case, you return the number itself (that is, 1 if x is 1 and 0 if x is
>> 0).
>>
>> Stefano
>
> Many people forget (or don't know) the series starts:
>
> Fib(0)=0
> Fib(1)=1
> Fib(2)=1
> ....
> So when x < 2 then Fib=x
> These initial conditions are important for doing algebraic forms for
> the series.

The first time I saw this problem, I did the recursive thing, but I
just _had_ to use #inject, so for a full list...

n = 10
(0...n-1).inject([0,1]) {|a, i| a.push(a[-2] + a[-1])}

Of course if you only want the nth number you can #shift inside the
#inject, and always keep the array size 2.

Todd