aoc_day1.ex

defmodule AOC do
  def compare([first, second], acc) when first == second, do: acc + first
  def compare(_, acc), do: acc
  def calculate(nums) do
    nums
    |> String.split("", trim: true)
    |> Enum.map(&String.to_integer/1)
    |> Stream.cycle
    |> Stream.take(String.length(nums) + 1)
    |> Stream.chunk_every(2, 1, :discard)
    |> Enum.to_list
    |> Enum.reduce(0, &compare/2)
  end
end

"4443"
|> AOC.calculate
|> IO.inspect