roman.rb

#!/usr/bin/env ruby

module RomanNumeral
  BRUTE_VALUE_MAP = {
    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'
  }

  def to_roman
    remainder = self
    result = ''
    pairs = BRUTE_VALUE_MAP.to_a.sort.reverse
    pairs.each do |value, numeral|
      while remainder >= value
        result += numeral
        remainder -= value
      end
    end
    result
  end
end

class Fixnum
  include RomanNumeral
end

test_cases = {
  1 => 'I',
  2 => 'II',
  3 => 'III',
  4 => 'IV',
  5 => 'V',
  6 => 'VI',
  7 => 'VII',
  8 => 'VIII',
  9 => 'IX',
  10 => 'X',
  50 => 'L',
  100 => 'C',
  500 => 'D',
  1000 => 'M',
  31 => 'XXXI',
  148 => 'CXLVIII',
  294 => 'CCXCIV',
  312 => 'CCCXII',
  421 => 'CDXXI',
  528 => 'DXXVIII',
  621 => 'DCXXI',
  782 => 'DCCLXXXII',
  870 => 'DCCCLXX',
  911 => 'CMXI',
  941 => 'CMXLI',
  1043 => 'MXLIII',
  1110 => 'MCX',
  1226 => 'MCCXXVI',
  1301 => 'MCCCI',
  1485 => 'MCDLXXXV',
  1509 => 'MDIX',
  1607 => 'MDCVII',
  1754 => 'MDCCLIV',
  1832 => 'MDCCCXXXII',
  1993 => 'MCMXCIII',
  2074 => 'MMLXXIV',
  2152 => 'MMCLII',
  2212 => 'MMCCXII',
  2343 => 'MMCCCXLIII',
  2499 => 'MMCDXCIX',
  2574 => 'MMDLXXIV',
  2646 => 'MMDCXLVI',
  2723 => 'MMDCCXXIII',
  2892 => 'MMDCCCXCII',
  2975 => 'MMCMLXXV',
  3051 => 'MMMLI',
  3185 => 'MMMCLXXXV',
  3250 => 'MMMCCL',
  3313 => 'MMMCCCXIII',
  3408 => 'MMMCDVIII',
  3501 => 'MMMDI',
  3610 => 'MMMDCX',
  3743 => 'MMMDCCXLIII',
  3844 => 'MMMDCCCXLIV',
  3888 => 'MMMDCCCLXXXVIII',
  3940 => 'MMMCMXL',
  3999 => 'MMMCMXCIX'
}

test_cases.each do |value, numeral|
  result = value.to_roman
  if result == numeral
    puts "OK: #{value} -> #{result}"
  else
    puts "FAIL: #{value} -> #{result} (expected #{numeral})"
  end
end