Fibonacci.rb

#!/usr/bin/env ruby

# Public: Calculates the nth Fibonacci number using either a memoized or
#         non-memoized functionality
#
# Examples
#
#   fib = Fibonacci.new
#   fib.get_fib 10
#   # => 55
class Fibonacci
  # Public: Initialize the array of fibonacci numbers for the memoized
  #         implementation
  def initialize
    # We must start the fib_array with 0 because the index of the number
    # represents the nth fibonacci number, and there is no 0th fibonacci number
    @fib_array = [0, 1]
  end

  # Public: A memoized implementation of calcutating a fibonacci number
  #
  # n - the fibonacci number to be calculated
  #
  # Examples
  #
  #   fib = Fibonacci.new
  #   fib.get_fib 7
  #   # => 13
  def get_fib(n)
    return @fib_array[n] unless @fib_array[n].nil?

    fib_value = get_fib(n - 1) + get_fib(n - 2)

    @fib_array.push fib_value
    fib_value
  end

  # Public: A non-memoized implementation of calcutating a fibonacci number
  #
  # n - the fibonacci number to be calculated
  #
  # Examples
  #
  #   fib = Fibonacci.new
  #   fib.get_fib_old 7
  #   # => 13
  def get_fib_old(n)
    return n if n < 2

    get_fib_old(n - 1) + get_fib_old(n - 2)
  end
end