Fibonacci sequence in Ruby (recursion)

Question

I\'m trying to implement the following function, but it keeps giving me the stack level too deep (SystemStackError) error.

Any ideas what the problem mi

Answer 1

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)