fixnum_to_roman.rb

class Fixnum
  def to_roman
    [].tap do |res|
      a, b = self.divmod(10) ; res << ([''] + %w(I II III IV V VI VII VIII IX))[b]
      a, b =    a.divmod(10) ; res << ([''] + %w(X XX XXX XL L LX LXX LXXX XC))[b]
      a, b =    a.divmod(10) ; res << ([''] + %w(C CC CCC CD D DC DCC DCCC CM))[b]
      a, b =    a.divmod(10) ; res << ([''] + %w(M MM MMM Mv v vM vMM vMMM Mx))[b]
      a, b =    a.divmod(10) ; res << ([''] + %w(x xx xxx xl l lx lxx lxxx xc))[b]
      a, b =    a.divmod(10) ; res << ([''] + %w(c cc ccc cd d dc dcc dccc cm))[b]
    end.reverse.join
  end
end

# class Fixnum
#   def to_roman
#     raise "too big" if self > 10_999
#     roman_additive_to_roman_substractive(self.to_roman_additive)
#   end
#
#   def to_roman_additive
#     tens,      units    = self    .divmod(10)
#     hundreds,  tens     = tens    .divmod(10)
#     thousands, hundreds = hundreds.divmod(10)
#
#     'M'*thousands + 'C'*hundreds + 'X'*tens + 'I'*units
#   end
#
#   def roman_additive_to_roman_substractive(s)
#     s.
#       gsub('IIIIIIIII', 'IX').
#       gsub('IIIII',      'V').
#       gsub('IIII',      'IV').
#       gsub('XXXXXXXXX', 'XC').
#       gsub('XXXXX',      'L').
#       gsub('XXXX',      'XL').
#       gsub('CCCCCCCCC', 'CM').
#       gsub('CCCCC',      'D').
#       gsub('CCCC',      'CD')
#   end
# end

fixnum_to_roman_test.rb

require 'minitest/autorun'
require_relative 'fixnum_to_roman'

class RomanTest < MiniTest::Unit::TestCase

  def test_0
    assert_equal '', 0.to_roman
  end

  def test_1
    assert_equal 'I', 1.to_roman
  end

  def test_2
    assert_equal 'II', 2.to_roman
  end

  def test_3
    assert_equal 'III', 3.to_roman
  end

  def test_4
    assert_equal 'IV', 4.to_roman
  end

  def test_5
    assert_equal 'V', 5.to_roman
  end

  def test_6
    assert_equal 'VI', 6.to_roman
  end

  def test_9
    assert_equal 'IX', 9.to_roman
  end

  def test_10
    assert_equal 'X', 10.to_roman
  end

  def test_27
    assert_equal 'XXVII', 27.to_roman
  end

    def test_50
      assert_equal 'L', 50.to_roman
    end
    #

    def test_48
    assert_equal 'XLVIII', 48.to_roman
  end

  def test_59
    assert_equal 'LIX', 59.to_roman
  end

  def test_93
    assert_equal 'XCIII', 93.to_roman
  end

  def test_141
    assert_equal 'CXLI', 141.to_roman
  end

  def test_163
    assert_equal 'CLXIII', 163.to_roman
  end

  def test_402
    assert_equal 'CDII', 402.to_roman
  end

  def test_575
    assert_equal 'DLXXV', 575.to_roman
  end

  def test_911
    assert_equal 'CMXI', 911.to_roman
  end

  def test_1100
    assert_equal 'MC', 1100.to_roman
  end

  def test_1024
    assert_equal 'MXXIV', 1024.to_roman
  end

  def test_3000
    assert_equal 'MMM', 3000.to_roman
  end

  def test_5001_to_8888
    assert_equal 'vI', 5001.to_roman
    assert_equal 'vDLV', 5555.to_roman
    assert_equal 'vMMMDCCCLXXXVIII', 8888.to_roman
  end

  def test_10_000_to_39_999
    assert_equal 'x', 10_000.to_roman
    assert_equal 'xxxMxCMXCIX', 39_999.to_roman
  end

  def test_50_000
    assert_equal    'l', 50_000.to_roman
    assert_equal 'lxxx', 80_000.to_roman
    assert_equal   'xc', 90_000.to_roman
  end

  def test_100_000_to_
    assert_equal 'c', 100_000.to_roman
  end
end