roman_numerals.rb

require 'rubygems'
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
    ROMANS.detect do |roman, arabic|
      diff = self - arabic
      return "#{roman}#{diff.to_roman}" if diff >= 0
    end
  end
end

describe "Roman numerals" do

  # Is this wrong?
  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
  }
  
  TRANSFORMATIONS.each do |roman, arabic|
    it "transforms #{arabic} to #{roman}" do
      arabic.to_roman.should == roman.to_s
    end
  end

end