Advent of Code 2024

aoc_helpers_path =
  __ENV__.file
  |> String.split("#")
  |> hd()
  |> Path.dirname()
  |> then(fn dir ->
    [dir, "..", "aoc_helpers"]
  end)
  |> Path.join()

Mix.install([
  {:aoc_helpers, path: aoc_helpers_path}
])

Day 19

import AocHelpers

Kino.configure(inspect: [charlists: :as_lists])

input = download_puzzle(2024, 19, cookie: System.get_env("AOC_COOKIE"))

sample = """
r, wr, b, g, bwu, rb, gb, br

brwrr
bggr
gbbr
rrbgbr
ubwu
bwurrg
brgr
bbrgwb
"""

Kino.nothing()

defmodule Day19 do
  def parse(input) do
    [towels, designs] =
      input
      |> blocks()

    towels = towels |> String.split(", ")
    designs = designs |> lines()

    {towels, designs}
  end

  def can_make?(towels, design) do
    towels
    |> Enum.any?(&can_make?(towels, design, &1))
  end

  def can_make?(towels, design, towel) do
    case design do
      ^towel <> "" ->
        true

      ^towel <> rest ->
        towels
        |> Enum.any?(&amp;can_make?(towels, rest, &amp;1))

      _ ->
        false
    end
  end

  def count_arrangements(towels, design, towel, cache) do
    if Map.has_key?(cache, {design, towel}) do
      {cache, Map.get(cache, {design, towel})}
    else
      {cache, n} =
        case design do
          ^towel <> "" ->
            {cache, 1}

          ^towel <> rest ->
            towels
            |> Enum.reduce({cache, 0}, fn towel, {cache, sum} ->
              {cache, n} = count_arrangements(towels, rest, towel, cache)
              {cache, sum + n}
            end)

          _ ->
            {cache, 0}
        end

      cache = Map.put(cache, {design, towel}, n)
      {cache, n}
    end
  end
end

import Day19

Part 1

{towels, designs} =
  input
  |> parse()

designs
|> Enum.count(& can_make?(towels, &1))

Part 2

{towels, designs} =
  input
  |> parse()

designs
|> Enum.reduce({Map.new(), 0}, fn design, {cache, sum} ->
  towels
  |> Enum.reduce({cache, sum}, fn towel, {cache, sum} ->
    {cache, n} = count_arrangements(towels, design, towel, cache)
    {cache, sum + n}
  end)
end)
|> elem(1)