2024 day 18, part 2

Okay now that I know the answer, I can write an implementation that doesn't suck

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=452%20stars&style=for-the-badge&color=green" alt="452 stars" /></p>
-<p><a href="./lib/y2024/"><img src="https://img.shields.io/static/v1?label=2024&message=33%20stars&style=for-the-badge&color=yellow" alt="33 stars" /></a><br />
+<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 />
 <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=33%20stars&style=for-the-badge&color=yellow" alt="33 stars" /><!-- stars 2024 end -->
+<!-- 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 -->
 
 ## Benchmarks
 
@@ -47,4 +47,5 @@ day 16, part 1         12.91       77.43 ms     ±5.49%       77.14 ms       86.
 day 16, part 2         13.07       76.51 ms     ±5.00%       76.09 ms       85.69 ms
 day 17, part 1       45.64 K       21.91 μs    ±15.81%       21.17 μs       37.50 μs
 day 18, part 1          0.27         3.73 s     ±0.03%         3.73 s         3.73 s
+day 18, part 2        0.0250        39.94 s     ±0.00%        39.94 s        39.94 s
 ```

lib/y2024/day18.ex

@@ -3,7 +3,7 @@ defmodule Y2024.Day18 do
 
   alias Advent.PathGrid
 
-  def part1(bytes, size \\ 50, byte_num \\ 1024) do
+  def part1(bytes, size \\ 70, byte_num \\ 1024) do
     fallen = Enum.take(bytes, byte_num)
 
     graph =
@@ -14,13 +14,17 @@ defmodule Y2024.Day18 do
     length(Graph.get_shortest_path(graph, {0, 0}, {size, size})) - 1
   end
 
-  # @doc """
-  # iex> Day18.part2("update or delete me")
-  # "update or delete me"
-  # """
-  # def part2(input) do
-  #   input
-  # end
+  def part2(bytes, size \\ 70) do
+    Enum.reduce_while(bytes, empty_grid({0, 0}, {size, size}), fn {row, col}, graph ->
+      graph = PathGrid.add_wall(graph, {row, col})
+
+      if Graph.get_shortest_path(graph, {0, 0}, {size, size}) == nil do
+        {:halt, "#{row},#{col}"}
+      else
+        {:cont, graph}
+      end
+    end)
+  end
 
   @doc """
   iex> Day18.parse_input("5,4\\n4,2\\n4,5\\n3,0\\n")
@@ -58,5 +62,5 @@ defmodule Y2024.Day18 do
   end
 
   def part1_verify, do: input() |> parse_input() |> part1(70, 1024)
-  # def part2_verify, do: input() |> parse_input() |> part2()
+  def part2_verify, do: input() |> parse_input() |> part2()
 end

test/y2024/day18_test.exs

@@ -7,8 +7,14 @@ defmodule Y2024.Day18Test do
     assert test_data() |> Day18.parse_input() |> Day18.part1(6, 12) == 22
   end
 
+  test "part2" do
+    assert test_data() |> Day18.parse_input() |> Day18.part2(6) == "6,1"
+  end
+
   test "verification, part 1", do: assert(Day18.part1_verify() == 436)
-  # test "verification, part 2", do: assert(Day18.part2_verify() == "update or delete me")
+
+  @tag timeout: :infinity
+  test "verification, part 2", do: assert(Day18.part2_verify() == "61,50")
 
   def test_data(), do: File.read!("test/y2024/input/day18/sample.txt")
 end