2024 day 13, 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=443%20stars&style=for-the-badge&color=green" alt="443 stars" /></p>
-<p><a href="./lib/y2024/"><img src="https://img.shields.io/static/v1?label=2024&message=24%20stars&style=for-the-badge&color=orange" alt="24 stars" /></a><br />
+<p><img src="https://img.shields.io/static/v1?label=Total&message=444%20stars&style=for-the-badge&color=green" alt="444 stars" /></p>
+<p><a href="./lib/y2024/"><img src="https://img.shields.io/static/v1?label=2024&message=25%20stars&style=for-the-badge&color=yellow" alt="25 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 />
 <a href="./lib/y2022/"><img src="https://img.shields.io/static/v1?label=2022&message=%E2%AD%90%EF%B8%8F%2050%20stars%20%E2%AD%90%EF%B8%8F&style=for-the-badge&color=brightgreen" alt="50 stars" /></a><br />
 <a href="./lib/y2021/"><img src="https://img.shields.io/static/v1?label=2021&message=46%20stars&style=for-the-badge&color=green" alt="46 stars" /></a><br />

lib/y2024/README.md

@@ -2,7 +2,7 @@
 
 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=24%20stars&style=for-the-badge&color=orange" alt="24 stars" /><!-- stars 2024 end -->
+<!-- stars 2024 start --><img src="https://img.shields.io/static/v1?label=2024&message=25%20stars&style=for-the-badge&color=yellow" alt="25 stars" /><!-- stars 2024 end -->
 
 ## Benchmarks
 
@@ -38,4 +38,5 @@ day 11, part 1        838.21        1.19 ms     ±4.86%        1.21 ms        1.
 day 11, part 2         19.52       51.22 ms     ±1.86%       51.26 ms       53.37 ms
 day 12, part 1          7.16      139.70 ms     ±1.82%      139.22 ms      144.95 ms
 day 12, part 2          6.84      146.22 ms     ±1.32%      145.82 ms      151.25 ms
+day 13, part 1          4.91      203.63 ms     ±0.46%      203.49 ms      206.75 ms
 ```

lib/y2024/day13.ex

@@ -0,0 +1,77 @@
+defmodule Y2024.Day13 do
+  use Advent.Day, no: 13
+
+  @doc """
+  iex> Day13.part1([%{buttons: %{a: %{x: 94, y: 34, cost: 3}, b: %{x: 22, y: 67, cost: 1}}, prize: %{x: 8400, y: 5400}}])
+  280
+  """
+  def part1(machines) do
+    machines
+    |> Enum.map(&find_solution/1)
+    |> Enum.reduce(0, fn
+      %{a: a, b: b}, acc -> acc + a.tokens + b.tokens
+      nil, acc -> acc
+    end)
+  end
+
+  # @doc """
+  # iex> Day13.part2("update or delete me")
+  # "update or delete me"
+  # """
+  # def part2(input) do
+  #   input
+  # end
+
+  @doc """
+  iex> Day13.find_solution(%{buttons: %{a: %{x: 94, y: 34, cost: 3}, b: %{x: 22, y: 67, cost: 1}}, prize: %{x: 8400, y: 5400}})
+  %{a: %{presses: 80, tokens: 240}, b: %{presses: 40, tokens: 40}}
+  """
+  def find_solution(%{buttons: %{a: a, b: b}, prize: prize}) do
+    a_presses = Enum.min([100, div(prize.x, a.x), div(prize.y, a.y)])
+    b_presses = Enum.min([100, div(prize.x, b.x), div(prize.y, b.y)])
+
+    result =
+      for(
+        a_press <- 0..a_presses,
+        b_press <- 0..b_presses,
+        do: {a_press, b_press, a.cost * a_press + b.cost * b_press}
+      )
+      |> Enum.sort_by(fn {_, _, cost} -> cost end)
+      |> Enum.find(fn {a_press, b_press, _cost} ->
+        a_press * a.x + b_press * b.x == prize.x && a_press * a.y + b_press * b.y == prize.y
+      end)
+
+    if result do
+      %{
+        a: %{tokens: a.cost * elem(result, 0), presses: elem(result, 0)},
+        b: %{tokens: b.cost * elem(result, 1), presses: elem(result, 1)}
+      }
+    end
+  end
+
+  @doc """
+  iex> Day13.parse_input("Button A: X+94, Y+34\\nButton B: X+22, Y+67\\nPrize: X=8400, Y=5400")
+  [%{buttons: %{a: %{x: 94, y: 34, cost: 3}, b: %{x: 22, y: 67, cost: 1}}, prize: %{x: 8400, y: 5400}}]
+  """
+  def parse_input(input) do
+    input
+    |> String.split("\n\n", trim: true)
+    |> Enum.map(fn machine ->
+      [a, b, prize] = String.split(machine, "\n", trim: true)
+      %{buttons: %{a: parse_button(a, 3), b: parse_button(b, 1)}, prize: parse_prize(prize)}
+    end)
+  end
+
+  defp parse_button(string, cost) do
+    <<"Button ", _::binary-1, ": X+", x::binary-2, ", Y+", y::binary-2>> = string
+    %{cost: cost, x: String.to_integer(x), y: String.to_integer(y)}
+  end
+
+  defp parse_prize(string) do
+    [[x], [y]] = Regex.scan(~r/\d+/, string)
+    %{x: String.to_integer(x), y: String.to_integer(y)}
+  end
+
+  def part1_verify, do: input() |> parse_input() |> part1()
+  # def part2_verify, do: input() |> parse_input() |> part2()
+end

test/y2024/day13_test.exs

@@ -0,0 +1,8 @@
+defmodule Y2024.Day13Test do
+  use ExUnit.Case, async: true
+  alias Y2024.Day13
+  doctest Day13
+
+  test "verification, part 1", do: assert(Day13.part1_verify() == 27157)
+  # test "verification, part 2", do: assert(Day13.part2_verify() == "update or delete me")
+end