2021 Day 2

Mix.install([
  {:kino, "~> 0.6.1"},
  {:kino_vega_lite, "~> 0.1.1"}
])

alias VegaLite, as: Vl

Input

raw_input = Kino.Input.textarea("Problem Input")

Parse

input =
  Kino.Input.read(raw_input)
  |> String.trim()
  |> String.split("\n")
  |> Enum.map(&String.split(&1, " "))
  |> Enum.map(&List.to_tuple/1)
  |> Enum.map(fn {direction, distance} ->
    {String.to_atom(direction), String.to_integer(distance)}
  end)

Part 1

Count the number of times the depth increased

input
|> Enum.reduce({0, 0}, fn command, {horizontal, depth} ->
  case command do
    {:forward, distance} -> {horizontal + distance, depth}
    {:down, distance} -> {horizontal, depth + distance}
    {:up, distance} -> {horizontal, depth - distance}
  end
end)
|> Tuple.to_list()
|> Enum.product()

Part 2

Count the the increases in a sliding three wide window of depths

input
|> Enum.reduce({0, 0, 0}, fn command, {horizontal, depth, aim} ->
  case command do
    {:forward, distance} -> {horizontal + distance, depth + aim * distance, aim}
    {:down, distance} -> {horizontal, depth, aim + distance}
    {:up, distance} -> {horizontal, depth, aim - distance}
  end
end)
|> Tuple.to_list()
|> Enum.take(2)
|> Enum.product()