Roman Numerals

gistfile1.rb

class RomanNumerals
  NUM_TO_ROMAN = { 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' }

  class << self

    def to_roman(num)
      NUM_TO_ROMAN.each_with_object("") { |(k,v), mem|  mem << (v * (num / k)); num = num % k  }
    end

    def from_roman(roman)
      num = 0
      transpose = Hash[NUM_TO_ROMAN.map{ |k, v| [v,k] }]
      two_val_romans = /#{NUM_TO_ROMAN.values.select { |v| v.size == 2}.join("|")}/
      roman = roman.gsub(two_val_romans) { |word| num += transpose[word]; "" }
      roman.chars.to_a.inject(num) { |n,chr| n += transpose[chr].to_i }
    end
  end

end

RomanNumerals.to_roman(1540) # => "MDXL"
RomanNumerals.to_roman(1590) # => "MDXC"
RomanNumerals.from_roman("MDXL") # => 1540
RomanNumerals.from_roman("MDXC") # => 1590
RomanNumerals.from_roman("XIX") # => 19