Fibonacci sequence in Ruby (recursion)

Here is something I came up with, I find this more straight forward.

def fib(n)
  n.times.each_with_object([0,1]) { |num, obj| obj << obj[-2] + obj[-1] }
end
fib(10)

Try this

def fibonacci( n )
  return  n  if ( 0..1 ).include? n
  ( fibonacci( n - 1 ) + fibonacci( n - 2 ) )
end
puts fibonacci( 5 )
# => 5

check this post too Fibonacci One-Liner

and more .. https://web.archive.org/web/20120427224512/http://en.literateprograms.org/Fibonacci_numbers_(Ruby)

You have now been bombarded with many solutions :)

regarding problem in ur solution

you should return n if its 0 or 1

and add last two numbers not last and next

New Modified version

def fibonacci( n )
    return  n  if n <= 1 
    fibonacci( n - 1 ) + fibonacci( n - 2 )
end 
puts fibonacci( 10 )
# => 55

One liner

def fibonacci(n)
   n <= 1 ? n :  fibonacci( n - 1 ) + fibonacci( n - 2 ) 
end
puts fibonacci( 10 )
# => 55

This approach is fast and makes use of memoization:

fib = Hash.new {|hash, key| hash[key] = key < 2 ? key : hash[key-1] + hash[key-2] }

fib[123] # => 22698374052006863956975682

In case you're wondering about how this hash initialization works read here:

https://ruby-doc.org/core/Hash.html#method-c-new

Linear

module Fib
  def self.compute(index)
    first, second = 0, 1
    index.times do
      first, second = second, first + second
    end
    first
  end
end

Recursive with caching

module Fib
  @@mem = {}
  def self.compute(index)
    return index if index <= 1

    @@mem[index] ||= compute(index-1) + compute(index-2)
  end
end

Closure

module Fib
  def self.compute(index)
    f = fibonacci
    index.times { f.call }
    f.call
  end

  def self.fibonacci
    first, second = 1, 0
    Proc.new {
      first, second = second, first + second
      first
    }
  end
end

None of these solutions will crash your system if you call Fib.compute(256)