Day 2

Input

Mix.install([
  {:kino, "~> 0.4.1"}
])

inputwidget = Kino.Input.textarea("Enter your AOC input for the day here")

input =
  Kino.Input.read(inputwidget)
  |> String.split("\n")
  |> Enum.map(fn step ->
    [direction, count] = String.split(step)
    {direction, String.to_integer(count)}
  end)

Part 1

Submarine starts from 0, 0 horizontal and depth position.

• forward moves horizontally (adds to horizontal position)
• up moves up in depth (subtracts from depth)
• down moves down in depth (adds to depth)

{h, d} =
  input
  |> Enum.reduce({0, 0}, fn {direction, count}, {h, d} ->
    case direction do
      "forward" ->
        {h + count, d}

      "up" ->
        {h, d - count}

      "down" ->
        {h, d + count}

      _ ->
        {h, d}
    end
  end)

h * d

Part 2

Submarine starts with 0, 0 horizontal and depth position, and 0 aim

• forward moves horizontally and aim*count in depth (h + count, d + count x aim)
• up reduces aim (aim - count)
• down increases aim (aim + count)

{h, d, _} =
  input
  |> Enum.reduce({0, 0, 0}, fn {direction, count}, {h, d, a} ->
    case direction do
      "forward" ->
        {h + count, d + count * a, a}

      "up" ->
        {h, d, a - count}

      "down" ->
        {h, d, a + count}

      _ ->
        {h, d, a}
    end
  end)

h * d