Convert Arabic Roman Numbers with Ruby

roman_numerals_in_ruby.rb

class Fixnum
  # Unique + special roman numerals
  ROMANS = {  1000: 'M', 900: 'CM', 500: 'D', 400: 'CD', 100: 'C',
              90: 'XC', 50: 'L', 40: 'XL', 10: 'X', 9: 'IX', 
              5: 'V', 4: 'IV', 1: 'I' }.freeze
  
  def to_roman
    ROMANS[self] || divide_and_conquer_roman(self)
  end

  private

  def divide_and_conquer_roman(number)
    ROMANS.reduce('') do | numeral, (arabic, roman) |
      quotient, number = number.divmod(arabic)
      numeral << roman * quotient
    end
  end
end