2024 day 19, part 1

README.md

@@ -5,8 +5,8 @@
 My Elixir solutions for [Advent of Code](https://adventofcode.com/) (all years).
 
 <!-- stars start -->
-<p><img src="https://img.shields.io/static/v1?label=Total&message=453%20stars&style=for-the-badge&color=green" alt="453 stars" /></p>
-<p><a href="./lib/y2024/"><img src="https://img.shields.io/static/v1?label=2024&message=34%20stars&style=for-the-badge&color=yellow" alt="34 stars" /></a><br />
+<p><img src="https://img.shields.io/static/v1?label=Total&message=454%20stars&style=for-the-badge&color=green" alt="454 stars" /></p>
+<p><a href="./lib/y2024/"><img src="https://img.shields.io/static/v1?label=2024&message=35%20stars&style=for-the-badge&color=yellow" alt="35 stars" /></a><br />
 <a href="./lib/y2023/"><img src="https://img.shields.io/static/v1?label=2023&message=44%20stars&style=for-the-badge&color=green" alt="44 stars" /></a><br />
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lib/y2024/README.md

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 My Elixir solutions for [Advent of Code 2024](https://adventofcode.com/2024).
 
-<!-- stars 2024 start --><img src="https://img.shields.io/static/v1?label=2024&message=34%20stars&style=for-the-badge&color=yellow" alt="34 stars" /><!-- stars 2024 end -->
+<!-- stars 2024 start --><img src="https://img.shields.io/static/v1?label=2024&message=35%20stars&style=for-the-badge&color=yellow" alt="35 stars" /><!-- stars 2024 end -->
 
 ## Benchmarks
 
@@ -48,4 +48,5 @@ day 16, part 2         13.07       76.51 ms     ±5.00%       76.09 ms       85.
 day 17, part 1       45.64 K       21.91 μs    ±15.81%       21.17 μs       37.50 μs
 day 18, part 1         22.53       44.38 ms     ±5.11%       44.48 ms       48.54 ms
 day 18, part 2          4.04      247.58 ms     ±3.18%      247.68 ms      260.90 ms
+day 19, part 1         19.46       51.38 ms     ±1.08%       51.16 ms       53.08 ms
 ```

lib/y2024/day19.ex

@@ -0,0 +1,45 @@
+defmodule Y2024.Day19 do
+  use Advent.Day, no: 19
+
+  def part1(%{from: from_towels, to: to_towels}) do
+    Enum.count(to_towels, fn to ->
+      can_make?(to, from_towels)
+    end)
+  end
+
+  # @doc """
+  # iex> Day19.part2("update or delete me")
+  # "update or delete me"
+  # """
+  # def part2(input) do
+  #   input
+  # end
+
+  defp can_make?(to, from_towels) do
+    find_towel_list([{to, []}], from_towels) != nil
+  end
+
+  defp find_towel_list([], _from_towels), do: nil
+  defp find_towel_list([{[], made} | _rest], _from_towels), do: Enum.reverse(made)
+
+  defp find_towel_list([{to, made} | rest], from_towels) do
+    new =
+      from_towels
+      |> Enum.filter(fn from -> List.starts_with?(to, from) end)
+      |> Enum.map(fn from -> {Enum.drop(to, length(from)), [from | made]} end)
+
+    find_towel_list(new ++ rest, from_towels)
+  end
+
+  def parse_input(input) do
+    [from, to] = String.split(input, "\n\n", trim: true)
+
+    %{
+      from: String.split(from, ", ") |> Enum.map(&String.graphemes/1),
+      to: String.split(to, "\n", trim: true) |> Enum.map(&String.graphemes/1)
+    }
+  end
+
+  def part1_verify, do: input() |> parse_input() |> part1()
+  # def part2_verify, do: input() |> parse_input() |> part2()
+end

test/y2024/day19_test.exs

@@ -0,0 +1,31 @@
+defmodule Y2024.Day19Test do
+  use ExUnit.Case, async: true
+  alias Y2024.Day19
+  doctest Day19
+
+  @sample """
+  r, wr, b, g, bwu, rb, gb, br
+
+  brwrr
+  bggr
+  gbbr
+  rrbgbr
+  ubwu
+  bwurrg
+  brgr
+  bbrgwb
+  """
+
+  test "part1" do
+    assert Day19.parse_input(@sample) |> Day19.part1() == 6
+  end
+
+  test "parse_input" do
+    assert %{from: from, to: to} = Day19.parse_input(@sample)
+    assert [["r"], ["w", "r"] | _rest] = from
+    assert [["b", "r", "w", "r", "r"], ["b", "g", "g", "r"] | _rest] = to
+  end
+
+  test "verification, part 1", do: assert(Day19.part1_verify() == 285)
+  # test "verification, part 2", do: assert(Day19.part2_verify() == "update or delete me")
+end