Run-length encoding

rle.ex

defmodule RLE do
  defp run_length_encode(terms, encoding) do
    terms = Enum.map(terms, &encoding[&1])

    Enum.reduce(tl(terms), [{hd(terms), 1}], fn
      c, [{c, count} | rest] -> [{c, count + 1} | rest]
      c, [{c_prime, count} | rest] -> [{c, 1}, {c_prime, count} | rest]
    end)
    |> Enum.map(fn {c, count} -> "#{c}#{inspect(count)}" end)
    |> Enum.reverse()
    |> Enum.join()
  end
end