Roman Numerals

.gitignore

*.gem
.bundle
Gemfile.lock
pkg/*

README.md

Roman Numerals

Logic for dealing with Roman numerals.

License

The MIT License

Copyright (C) 2012 Victor Koronen

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Gemfile

source :rubygems

# Specify your gem's dependencies in roman_numerals.gemspec
gemspec

Guardfile

guard 'bundler' do
  watch('Gemfile')
  watch(/^.+\.gemspec/)
end

guard 'minitest' do
  watch(%r|^spec/(.*)_spec\.rb|)
  watch(%r|^lib/(.*)([^/]+)\.rb|)     { |m| "spec/#{m[1]}#{m[2]}_spec.rb" }
  watch(%r|^spec/spec_helper\.rb|)    { "spec" }
end

Rakefile

require 'bundler/gem_tasks'
require 'rake/testtask'

Rake::TestTask.new(:spec) do |t|
  t.libs << 'spec'
  t.test_files = FileList['spec/**/*_spec.rb']
end

task default: :spec

roman_numeral.rb

class RomanNumeral
  NUMERALS = {
    "I" => 1,
    "V" => 5,
    "X" => 10,
    "L" => 50,
    "C" => 100,
    "D" => 500,
    "M" => 1000
  }

  def initialize(number)
    if number.is_a? String
      number = parse_string number
    else
      number = number.to_i
    end

    if number < 0
      throw ArgumentError
    end

    @number = number
  end

  def to_i
    @number
  end

  def to_s
    return "" if @number == 0

    NUMERALS.each do |numeral, value|
      return numeral if @number == value
    end

    str = ""
    sum = 0

    NUMERALS.to_a.reverse.each do |numeral, value|
      while (@number - sum) >= value
        str += numeral
        sum += value
      end
    end

    str.gsub!("DCCCC", "CM")
    str.gsub!("LXXXX", "XC")
    str.gsub!("VIIII", "IX")
    str.gsub!("IIII", "IV")

    str
  end

private

  def valid_string?(str)
    /^[#{NUMERALS.keys.join}]*$/.match str
  end

  def parse_string(str)
    throw ArgumentError unless valid_string? str
    return 0 if str.empty?

    tokens = str.split(//).map{|t| NUMERALS[t] }

    number = 0
    buffer = last = tokens.shift

    tokens.each do |n|
      if n == last
        buffer += n
      elsif n < last
        number += buffer
        buffer = n
      elsif n > last
        number += n - buffer
        buffer = 0
      end

      last = n
    end

    if buffer > 0
      number += buffer
    end

    number
  end
end

roman_numeral_spec.rb

require 'spec_helper'
require 'roman_numeral'

describe RomanNumeral do
  describe "constructor" do
    it "accepts non-negative integers" do
      RomanNumeral.new(1).wont_be_nil
    end

    it "rejects negative integers" do
      lambda { RomanNumeral.new(-1) }.must_throw ArgumentError
    end

    it "accepts valid non-negative roman numerals as strings" do
      RomanNumeral.new("I").wont_be_nil
    end

    it "rejects invalid roman numerals as strings" do
      lambda { RomanNumeral.new("foobar") }.must_throw ArgumentError
    end
  end

  describe "#to_i" do
    it "handles valid integers" do
      RomanNumeral.new(0).to_i.must_equal 0
      RomanNumeral::NUMERALS.each do |_, value|
        RomanNumeral.new(value).to_i.must_equal value
      end
      RomanNumeral.new(17).to_i.must_equal 17
      RomanNumeral.new(4711).to_i.must_equal 4711
    end

    it "handles valid roman numerals" do
      RomanNumeral.new("").to_i.must_equal 0
      RomanNumeral::NUMERALS.each do |numeral, value|
        RomanNumeral.new(numeral).to_i.must_equal value
      end
      RomanNumeral.new("IV").to_i.must_equal 4
      RomanNumeral.new("IX").to_i.must_equal 9
      RomanNumeral.new("XVII").to_i.must_equal 17
      RomanNumeral.new("MCMXCIX").to_i.must_equal 1999
      RomanNumeral.new("MMMMDCCXI").to_i.must_equal 4711
    end
  end

  describe "#to_s" do
    it "handles valid integers" do
      RomanNumeral.new(0).to_s.must_equal ""
      RomanNumeral::NUMERALS.each do |numeral, value|
        RomanNumeral.new(value).to_s.must_equal numeral
      end
      RomanNumeral.new(4).to_s.must_equal "IV"
      RomanNumeral.new(9).to_s.must_equal "IX"
      RomanNumeral.new(17).to_s.must_equal "XVII"
      RomanNumeral.new(1999).to_s.must_equal "MCMXCIX"
      RomanNumeral.new(4711).to_s.must_equal "MMMMDCCXI"
    end

    it "handles valid roman numerals" do
      RomanNumeral.new("").to_s.must_equal ""
      RomanNumeral::NUMERALS.each do |numeral, _|
        RomanNumeral.new(numeral).to_s.must_equal numeral
      end
      RomanNumeral.new("IV").to_s.must_equal "IV"
      RomanNumeral.new("IX").to_s.must_equal "IX"
      RomanNumeral.new("XVII").to_s.must_equal "XVII"
      RomanNumeral.new("MCMXCIX").to_s.must_equal "MCMXCIX"
      RomanNumeral.new("MMMMDCCXI").to_s.must_equal "MMMMDCCXI"
    end
  end
end

roman_numerals.gemspec

# -*- encoding: utf-8 -*-

Gem::Specification.new do |s|
  s.name        = "roman_numerals"
  s.version     = "0.0.1"
  s.authors     = ["Victor Koronen"]
  s.email       = ["[email protected]"]
  s.homepage    = ""
  s.summary     = %q{Roman numerals}
  s.description = %q{Roman numerals}

  s.files         = `git ls-files`.split("\n")
  s.test_files    = `git ls-files -- {test,spec,features}/*`.split("\n")
  s.executables   = `git ls-files -- bin/*`.split("\n").map{ |f| File.basename(f) }
  s.require_paths = ["lib"]

  s.add_development_dependency "minitest"
  s.add_development_dependency "guard"
  s.add_development_dependency "guard-bundler"
  s.add_development_dependency "guard-minitest"
end

spec_helper.rb

require 'minitest/autorun'