roman_numerals.rb

require 'rspec'

class Fixnum
  ROMANS = { M: 1000, CM: 900, D: 500, CD: 400, C: 100, XC: 90, L: 50, XL: 40, X: 10, IX: 9, V: 5, IV: 4, I: 1 }

  def to_roman
    remaining_number = self
    ROMANS.inject ("") do | roman_str, current_number |
        times,remaining_number = remaining_number.divmod current_number[1]
        roman_str + current_number[0].to_s * times
    end
  end

  def to_roman_old
    roman = ""
    ROMANS.inject (self) do | remaining, number |
        quotient,rest = remaining.divmod number[1]
        roman += number[0].to_s * quotient
        rest
    end
    roman
  end

end

TRANSFORMATIONS = {
  I: 1, II: 2, III: 3, IV: 4, V: 5, VI: 6, VII: 7, VIII: 8, IX: 9, X: 10, XI: 11, XII: 12, XIV: 14, XV: 15,
  XIX: 19, XXXIX: 39, XL: 40, XLI: 41, L: 50, LXXXIX: 89, XC: 90, XCIX: 99, C: 100, CCCXCIX: 399, CD: 400,
  D: 500, DCCCXCIX: 899, CM: 900, M: 1000, MMXI: 2011
}

[:to_roman, :to_roman_old].each do |method|

  describe "Roman numerals '#{method}' implementation. " do

    TRANSFORMATIONS.each do |roman, arabic|
      it "transforms #{arabic} to #{roman}" do
        arabic.send(method).should == roman.to_s
      end
    end

  end
end