roman_numerals.rb

# adapted from solution found at https://codequizzes.wordpress.com/2013/10/27/converting-an-integer-to-a-roman-numeral/
class Integer

  def to_roman
    number = self
    result = ""
    roman_hash.keys.each do |divisor|
      quotient, modulus = number.divmod(divisor)
      result << roman_hash[divisor] * quotient
      number = modulus
    end 
    result
  end

  private

  def roman_hash
    {
      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"
    }
  end
end