compressor.rb

s = "stttartuuuup"

def compress(str)
  complex_object = str.chars.each_with_object({result: ""}) do |char, obj|
    if obj[:current] == char
      obj[:count] += 1
      next
    elsif obj[:current]
      obj[:result] += "#{obj[:count]}x#{obj[:current]}"
    end
    obj[:count] = 1
    obj[:current] = char
  end
  complex_object[:result] + "#{complex_object[:count]}x#{complex_object[:current]}"
end

puts compress(s)