Another roman numeral converter solution

roman_numeral_converter.rb

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

  def convert(input)
    sum = 0
    values = input.chars.map { |c| CONVERTS[c] }
    while v = values.shift
      if ! values.empty? && v < values.first
        sum += values.first - v
        values.shift
      else
        sum += v
      end
    end
    sum.to_s
  end
end