Advent of Code 2021

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Didn’t enjoy today’s one as much.

I was in a noisy room so I opted for a dictionary to represent my data structure instead of tuple (taxing to be remembering which position means what), thereby giving up my chance to use the amazing Tuple.product at the end. Anyhoo, my solutions down here:

defmodule AdventOfCode.Y2021.Day02 do
  @moduledoc """
  --- Day 2: Dive! ---
  Problem Link: https://adventofcode.com/2021/day/2
  """
  use AdventOfCode.Helpers.InputReader, year: 2021, day: 2

  def run_1, do: input!() |> parse() |> track_positions() |> then(&(&1.depth * &1.horizontal))
  def run_2, do: input!() |> parse() |> track_aims() |> then(&(&1.depth * &1.horizontal))

  def parse(data) do
    data
    |> String.split("\n")
    |> Enum.map(fn line ->
      [direction, value] = String.split(line, " ")
      {String.to_existing_atom(direction), String.to_integer(value)}
    end)
  end

  defp track_positions(directions) do
    directions
    |> Enum.reduce(%{horizontal: 0, depth: 0}, fn
      {:forward, v}, %{horizontal: horizontal} = acc -> %{acc | horizontal: horizontal + v}
      {:backward, v}, %{horizontal: horizontal} = acc -> %{acc | horizontal: horizontal - v}
      {:up, v}, %{depth: depth} = acc -> %{acc | depth: depth - v}
      {:down, v}, %{depth: depth} = acc -> %{acc | depth: depth + v}
    end)
  end

  defp track_aims(directions) do
    directions
    |> Enum.reduce(%{horizontal: 0, depth: 0, aim: 0}, fn
      {:forward, v}, %{horizontal: horizontal, depth: depth, aim: aim} = acc ->
        %{acc | horizontal: horizontal + v, depth: depth + aim * v}

      {:backward, v}, %{horizontal: horizontal} = acc ->
        %{acc | horizontal: horizontal - v}

      {:up, v}, %{aim: aim} = acc ->
        %{acc | aim: aim - v}

      {:down, v}, %{aim: aim} = acc ->
        %{acc | aim: aim + v}
    end)
  end
end
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