Advent of Code 2021 - Day 2

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

Instructions

https://adventofcode.com/2021/day/2

Get input

Paste the test input from the Day 2 instructions, your own input from Advent of Code, or copy from sdball 2021 Advent of Code Day 2 input

input = Kino.Input.textarea("Please paste your input:")

input =
  input
  |> Kino.Input.read()
  |> String.split("\n", trim: true)
  |> Enum.map(fn line ->
    case line do
      "forward " <> n -> {:forward, n |> String.to_integer()}
      "up " <> n -> {:up, n |> String.to_integer()}
      "down " <> n -> {:down, n |> String.to_integer()}
    end
  end)

Part 1

input
|> Enum.map(fn command ->
  case command do
    {:forward, n} -> {0, n}
    {:up, n} -> {-n, 0}
    {:down, n} -> {n, 0}
  end
end)
|> Enum.reduce(fn {new_depth, new_position}, {depth, position} ->
  {depth + new_depth, position + new_position}
end)
|> Tuple.product()

Part 1 - Refactor to only use reduce

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

Part 2

input
|> Enum.reduce({aim = 0, depth = 0, position = 0}, fn command, {aim, depth, position} ->
  case command do
    {:forward, n} -> {aim, depth + aim * n, position + n}
    {:down, n} -> {aim + n, depth, position}
    {:up, n} -> {aim - n, depth, position}
  end
end)
|> Tuple.delete_at(0)
|> Tuple.product()