compress.rb

class String
  include Enumerable

  def each
    each_char { |char| yield char }
  end
end

def compress_string(string)
  string.chunk{|x|x}.map { |char, ary| ary.length > 1 ? "#{char}#{ary.length}" : char }.join('')
end

puts compress_string("aaabbbaaaccc")