Roman Numerals

roman

class Integer
  Roman = 'IVXLCDM'
  def to_roman
    raise "Number too large" if self > 3999
    num = self
    num_size = Math.log10(num).to_i
    # for each num_size.downto(0),
    # get which character to display for that level.
    num_size.downto(0).map do |pow|
      mid = (pow * 2) + 1
      current = (num / (10 ** pow))
      num = num % (10 ** pow)
      # do this the long way then condense
      retval = ''
      mods = current % 5
      retval << Roman[mid-1] if mods == 4
      retval << Roman[mid + (current == 9 ? 1 : 0)] if current >= 4
      retval << (Roman[mid-1] * mods) if mods < 4
      retval
    end.join
  end
end