aoc2017_day1.ex

# http://adventofcode.com/2017/day/1

defmodule Day1 do
  def sum1(digits), do:
    digits
    |> Stream.concat(Enum.take(digits, 1))
    |> Stream.chunk_every(2, 1, :discard)
    |> Stream.filter(&match?([el, el], &1))
    |> Stream.map(&hd(&1))
    |> Enum.sum()

  def sum2(digits) do
    {first_half, second_half} = Enum.split(digits, digits |> Enum.count() |> div(2))

    first_half
    |> Stream.zip(second_half)
    |> Stream.filter(&match?({el, el}, &1))
    |> Stream.map(&elem(&1, 0))
    |> Enum.sum()
    |> Kernel.*(2)
  end

  def digits(string), do:
    string
    |> String.codepoints()
    |> Stream.map(&String.to_integer/1)
end


System.argv |> hd() |> Day1.digits() |> Day1.sum1() |> IO.inspect()
System.argv |> hd() |> Day1.digits() |> Day1.sum2() |> IO.inspect()