sequence.rb

  class Sequence
    def initialize(first_element)
      @current_element = first_element.to_s
    end

    def to_s
      @current_element
    end

    def next
      next_step
      self
    end

    private

    def next_step
      @current_element = @current_element.scan(/((\d)\2*)/).map{|element| "#{element.first.size}#{element.last}"}.join
    end
  end