run length compression

def compress_length(a)
  if a.length < 3
    return a
  end

  result = ""
  count = 1

  a.chars.each_with_index do |c, index|
    if c == a[index+1]
      count += 1
    else
      result << "#{c}#{count}"
      count = 1
    end
  end

  result.length >= a.length ? a : result
end