From a9519aebbf3ad9c23f7f37cdc0a75fe449e748d6 Mon Sep 17 00:00:00 2001
From: bluepython508 <bluepython508@users.noreply.github.io>
Date: Mon, 18 Dec 2023 09:19:27 +0000
Subject: [PATCH] Day 18

---
 lib/common.ex    |  4 +++
 lib/day10.ex     |  6 ++---
 lib/day16.ex     |  4 ---
 lib/day18.ex     | 67 ++++++++++++++++++++++++++++++++++++++++++++++++
 lib/mix_tasks.ex |  1 +
 tests/day18/1    | 14 ++++++++++
 tests/day18/1.1  |  1 +
 tests/day18/1.2  |  1 +
 8 files changed, 90 insertions(+), 8 deletions(-)
 create mode 100644 lib/day18.ex
 create mode 100644 tests/day18/1
 create mode 100644 tests/day18/1.1
 create mode 100644 tests/day18/1.2

diff --git a/lib/common.ex b/lib/common.ex
index 1de2d69..d7bea39 100644
--- a/lib/common.ex
+++ b/lib/common.ex
@@ -59,4 +59,8 @@ defmodule Aoc2023.Common do
 
   def repeat(_, 0), do: []
   def repeat(lst, n), do: Enum.concat(lst, repeat(lst, n - 1))
+
+  def add_vec({y, x}, {y_, x_}) do
+    {y + y_, x + x_}
+  end
 end
diff --git a/lib/day10.ex b/lib/day10.ex
index 75ffa9d..5ec14e0 100644
--- a/lib/day10.ex
+++ b/lib/day10.ex
@@ -13,8 +13,6 @@ defmodule Aoc2023.Day10 do
     ?S => []
   }
 
-  defp add_coords({y, x}, {y_, x_}), do: {y + y_, x + x_}
-
   defp path(s_conns, conns) do
     loop = fn recur, checked, checking ->
       checked_ = MapSet.union(checked, checking)
@@ -53,7 +51,7 @@ defmodule Aoc2023.Day10 do
         |> Enum.map(fn {c, x} ->
           {
             {y, x},
-            Map.get(@connections, c) |> Enum.map(pipe(add_coords({y, x})))
+            Map.get(@connections, c) |> Enum.map(pipe(add_vec({y, x})))
           }
         end)
       end)
@@ -71,7 +69,7 @@ defmodule Aoc2023.Day10 do
   end
 
   def part2({{sy, sx}, s_conns, grid, path}) do
-    s_dirs = s_conns |> Enum.map(pipe(add_coords({-sy, -sx}))) |> Enum.sort()
+    s_dirs = s_conns |> Enum.map(pipe(add_vec({-sy, -sx}))) |> Enum.sort()
     s_char = @connections |> Enum.find(fn {_, conns} -> Enum.sort(conns) == s_dirs end) |> elem(0)
     grid_ = grid |> list_map_at(sy, pipe(map_nth(0, pipe(List.replace_at(sx, s_char)))))
 
diff --git a/lib/day16.ex b/lib/day16.ex
index c141220..1a73fda 100644
--- a/lib/day16.ex
+++ b/lib/day16.ex
@@ -15,10 +15,6 @@ defmodule Aoc2023.Day16 do
     end
   end
 
-  defp add_vec({y, x}, {y_, x_}) do
-    {y + y_, x + x_}
-  end
-
   def parse(input) do
     input
     |> lines
diff --git a/lib/day18.ex b/lib/day18.ex
new file mode 100644
index 0000000..fab738e
--- /dev/null
+++ b/lib/day18.ex
@@ -0,0 +1,67 @@
+defmodule Aoc2023.Day18 do
+  require Integer
+  use Aoc2023
+
+  def parse(input) do
+    input
+    |> lines
+    |> Enum.map(fn line ->
+      [dir, n, color] =
+        Regex.run(~r/^([RDLU]) (\d+) \(#([0-9a-f]{6})\)$/, line, capture: :all_but_first)
+
+      {
+        dir |> String.to_charlist() |> head,
+        n |> String.to_integer(),
+        color
+      }
+    end)
+  end
+
+  defp simulate({pos, dist, points}, {dir, n}) do
+    p =
+      case dir do
+        :u -> {-n, 0}
+        :d -> {n, 0}
+        :r -> {0, n}
+        :l -> {0, -n}
+      end
+      |> add_vec(pos)
+
+    {p, dist + n, [p | points]}
+  end
+
+  defp area(perim, points),
+    # Shoelace formula
+    do:
+      Stream.zip(points, points |> Stream.cycle() |> Stream.drop(1))
+      |> Stream.map(fn {{y, x}, {y1, x1}} -> x * y1 - x1 * y end)
+      |> Enum.sum()
+      |> abs
+      |> then(&((&1 + perim) / 2))
+      |> trunc
+
+  defp run(instrs) do
+    {_, dist, points} = instrs |> Enum.reduce({{0, 0}, 2, [{0, 0}]}, &simulate(&2, &1))
+    area(dist, points)
+  end
+
+  def part1(input) do
+    run(for {dir, n, _} <- input, do: {case dir do
+      ?U -> :u
+      ?D -> :d
+      ?L -> :l
+      ?R -> :r
+    end, n})
+  end
+
+  def part2(input) do
+    run(for {_, _, <<len::binary-size(5), dir::integer>>} <- input do
+      {case dir do
+        ?0 -> :r
+        ?1 -> :d
+        ?2 -> :l
+        ?3 -> :u
+      end, String.to_integer(len, 16)}
+    end)
+  end
+end
diff --git a/lib/mix_tasks.ex b/lib/mix_tasks.ex
index 6b2299d..eb6837b 100644
--- a/lib/mix_tasks.ex
+++ b/lib/mix_tasks.ex
@@ -18,6 +18,7 @@ defmodule Mix.Tasks.Aoc do
   defp module(14), do: Aoc2023.Day14
   defp module(15), do: Aoc2023.Day15
   defp module(16), do: Aoc2023.Day16
+  defp module(18), do: Aoc2023.Day18
   # [MODULE INSERTION POINT]  
 
   defp base_dir(), do: System.get_env("AOC_BASE")
diff --git a/tests/day18/1 b/tests/day18/1
new file mode 100644
index 0000000..fc7612e
--- /dev/null
+++ b/tests/day18/1
@@ -0,0 +1,14 @@
+R 6 (#70c710)
+D 5 (#0dc571)
+L 2 (#5713f0)
+D 2 (#d2c081)
+R 2 (#59c680)
+D 2 (#411b91)
+L 5 (#8ceee2)
+U 2 (#caa173)
+L 1 (#1b58a2)
+U 2 (#caa171)
+R 2 (#7807d2)
+U 3 (#a77fa3)
+L 2 (#015232)
+U 2 (#7a21e3)
diff --git a/tests/day18/1.1 b/tests/day18/1.1
new file mode 100644
index 0000000..b2412e3
--- /dev/null
+++ b/tests/day18/1.1
@@ -0,0 +1 @@
+62
\ No newline at end of file
diff --git a/tests/day18/1.2 b/tests/day18/1.2
new file mode 100644
index 0000000..c4d07b7
--- /dev/null
+++ b/tests/day18/1.2
@@ -0,0 +1 @@
+952408144115
\ No newline at end of file