Advent Of Code Day 3

advent_day_3.ex

defmodule PresentDelivery do
  def input do
    "^><^>>>^"
  end

  def main(_) do
    input
    |> String.codepoints
    |> split_in_two
    |> Enum.map(&santa_path/1)
    |> Enum.concat
    |> Enum.uniq
    |> Enum.count
    |> IO.puts
  end

  def split_in_two(list) do
    santa = Enum.take_every(list, 2)
    [_ | newlist] = list
    robo = Enum.take_every(newlist, 2)
    [santa, robo]
  end

  def santa_path(input) do
    input
    |> Enum.reduce([[0,0]], fn(dir, acc) -> [next_point(List.first(acc), dir) | acc ] end)
  end

  def next_point(current, direction) do
    [x, y] = current
    case direction do
      "^" -> [x+1, y]
      "v" -> [x-1, y]
      "<" -> [x, y-1]
      ">" -> [x, y+1]
    end
  end

end