Day 19: Linen Layout

Mix.install([
  {:kino, "~> 0.14.2"}
])

Input

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

defmodule Day19Shared do
  def parse(input) do
    [patterns_raw, designs_raw] = input |> Kino.Input.read() |> String.split("\n\n")

    patterns = String.split(patterns_raw, ", ", trim: true) # |> Enum.map(&String.split(&1, "", trim: true))
    designs = String.split(designs_raw, "\n") # |> Enum.map(&String.split(&1, "", trim: true))
    
    {patterns, designs}
  end
end

# Day19Shared.parse(input)

Part 1

defmodule Day19Part1 do
  def process({patterns, designs}) do
    cache = :ets.new(:cache, [:set, :private])

    result =
      Enum.reduce(designs, 0, fn design, total ->
        total + do_count_matches(design, patterns, cache)
      end)

    :ets.delete(cache)

    result
  end

  defp do_count_matches(design, patterns, cache) do
    case :ets.lookup(cache, design) do
      [{_, result}] ->
        result

      [] ->
        result = calc_matches(design, patterns, cache)

        :ets.insert(cache, {design, result})

        result
    end
  end

  defp calc_matches("", _patterns, _cache), do: 0

  defp calc_matches(design, patterns, cache) do
    Enum.reduce(patterns, 0, fn pattern, acc ->
      cond do
        design == pattern ->
          acc + 1

        String.starts_with?(design, pattern) ->
          remaining = String.slice(design, String.length(pattern)..-1//1)
          acc + do_count_matches(remaining, patterns, cache)

        true ->
          acc
      end
    end)
  end
end

input |> Day19Shared.parse() |> Day19Part1.process()

# 243 is too low
# 244 is too low
# 260 is the right answer

Part 2