aoc.exs

  def decompress("") do
    ""
  end
  
  def handle_repeat(input) do
    re = ~r/(\d+)x(\d+)\)(.*)/
    [_, len, repeats, rest] = Regex.run re, input
    {section, remainder} = rest |> String.split_at(String.to_integer(len))
    (section |> String.duplicate(String.to_integer repeats))<> decompress(remainder)
  end

  def decompress(<< c ::binary-size(1), rest ::binary >>) do
    case c do
      "(" -> handle_repeat(rest)
      _ -> << c, decompress(rest) >>
    end
  end