defmodule LargestString do
  def largest_string(s) do
    s
    |> String.to_charlist()
    |> Enum.chunk_by(&(&1 in ~c"ab"))
    |> Enum.map(&sort_segment/1)
    |> List.flatten()
    |> List.to_string()
  end

  defp sort_segment([c | _] = segment) when c in ~c"ab" do
    Enum.sort(segment, :desc)
  end

  defp sort_segment(segment), do: segment
end