Advent of Code 2021, Day 2

Setup

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

input = Kino.Input.textarea("Input")

commands =
  input
  |> Kino.Input.read()
  |> String.split("\n")
  |> Enum.map(&String.split/1)
  |> Enum.map(fn [k, v] -> [k, String.to_integer(v)] end)

Part 1

[depth: d, horizontal: h] =
  Enum.reduce(commands, [depth: 0, horizontal: 0], fn command, [depth: d, horizontal: h] ->
    case command do
      ["forward", x] -> [depth: d, horizontal: h + x]
      ["up", x] -> [depth: d - x, horizontal: h]
      ["down", x] -> [depth: d + x, horizontal: h]
    end
  end)

d * h

Part 2

[depth: d, horizontal: h, aim: _] =
  Enum.reduce(commands, [depth: 0, horizontal: 0, aim: 0], fn command,
                                                              [depth: d, horizontal: h, aim: a] ->
    case command do
      ["forward", x] -> [depth: d + a * x, horizontal: h + x, aim: a]
      ["up", x] -> [depth: d, horizontal: h, aim: a - x]
      ["down", x] -> [depth: d, horizontal: h, aim: a + x]
    end
  end)

d * h