From 20501c08190aa7e8cc31223340fc9ee8a857f892 Mon Sep 17 00:00:00 2001
From: bluepython508 <bluepython508@users.noreply.github.io>
Date: Fri, 8 Dec 2023 14:08:39 +0000
Subject: [PATCH] Day 8

---
 lib/common.ex    |  3 +++
 lib/day8.ex      | 39 +++++++++++++++++++++++++++++++++++++++
 lib/mix_tasks.ex |  5 +++--
 tests/day8/1     |  9 +++++++++
 tests/day8/1.1   |  1 +
 tests/day8/2     |  5 +++++
 tests/day8/2.1   |  1 +
 tests/day8/3     | 10 ++++++++++
 tests/day8/3.2   |  1 +
 9 files changed, 72 insertions(+), 2 deletions(-)
 create mode 100644 lib/day8.ex
 create mode 100644 tests/day8/1
 create mode 100644 tests/day8/1.1
 create mode 100644 tests/day8/2
 create mode 100644 tests/day8/2.1
 create mode 100644 tests/day8/3
 create mode 100644 tests/day8/3.2

diff --git a/lib/common.ex b/lib/common.ex
index 14bc967..078dd7b 100644
--- a/lib/common.ex
+++ b/lib/common.ex
@@ -38,4 +38,7 @@ defmodule Aoc2023.Common do
 
   def head([head | _]), do: head
   def tail([_ | tail]), do: tail
+
+  def lcm(a, b), do: div(abs(a*b), Integer.gcd(a,b))
+  def lcm(ls), do: ls |> Enum.reduce(&lcm/2)
 end
diff --git a/lib/day8.ex b/lib/day8.ex
new file mode 100644
index 0000000..06eadd6
--- /dev/null
+++ b/lib/day8.ex
@@ -0,0 +1,39 @@
+defmodule Aoc2023.Day8 do
+  require Integer
+  use Aoc2023
+
+  def parse(input) do
+    input
+    |> String.split("\n\n")
+    |> then(fn [directions, map] ->
+      {
+        directions |> String.to_charlist() |> Enum.map(&%{?L => 0, ?R => 1}[&1]),
+        map
+        |> lines
+        |> Enum.map(&Regex.run(~r/(\w+) = \((\w+), (\w+)\)/, &1, capture: :all_but_first))
+        |> Enum.map(fn [src, dst1, dst2] -> {src, {dst1, dst2}} end)
+        |> Enum.into(%{})
+      }
+    end)
+  end
+
+  defp run({directions, map}, node, filter) do
+    directions
+    |> Stream.cycle()
+    |> Stream.scan(node, fn dir, pos -> map[pos] |> elem(dir) end)
+    |> Enum.find_index(filter)
+    |> Kernel.+(1)
+  end
+
+  def part1({directions, map}) do
+    if map["AAA"], do: run({directions, map}, "AAA", &(&1 == "ZZZ"))
+  end
+
+  def part2({directions, map}) do
+    map
+    |> Enum.map(pipe(elem(0)))
+    |> Enum.filter(pipe(String.ends_with?("A")))
+    |> Enum.map(&run({directions, map}, &1, pipe(String.ends_with?("Z"))))
+    |> lcm
+  end
+end
diff --git a/lib/mix_tasks.ex b/lib/mix_tasks.ex
index 208ae4e..d7d0a41 100644
--- a/lib/mix_tasks.ex
+++ b/lib/mix_tasks.ex
@@ -9,6 +9,7 @@ defmodule Mix.Tasks.Aoc do
   defp module(5), do: Aoc2023.Day5
   defp module(6), do: Aoc2023.Day6
   defp module(7), do: Aoc2023.Day7
+  defp module(8), do: Aoc2023.Day8
   # [MODULE INSERTION POINT]  
 
   defp base_dir(), do: System.get_env("AOC_BASE")
@@ -16,7 +17,7 @@ defmodule Mix.Tasks.Aoc do
   defp tests(day) do
     case File.ls(tests_dir(day)) do
       {:ok, paths} ->
-        paths |> Enum.filter(&(not String.contains?(&1, ".")))
+        paths |> Enum.filter(&(not String.contains?(&1, "."))) |> Enum.sort
 
       {:error, e} ->
         dbg(e)
@@ -203,4 +204,4 @@ defmodule Mix.Tasks.Aoc do
       {:noreply, state}
     end
   end
-end
\ No newline at end of file
+end
diff --git a/tests/day8/1 b/tests/day8/1
new file mode 100644
index 0000000..9029a1b
--- /dev/null
+++ b/tests/day8/1
@@ -0,0 +1,9 @@
+RL
+
+AAA = (BBB, CCC)
+BBB = (DDD, EEE)
+CCC = (ZZZ, GGG)
+DDD = (DDD, DDD)
+EEE = (EEE, EEE)
+GGG = (GGG, GGG)
+ZZZ = (ZZZ, ZZZ)
diff --git a/tests/day8/1.1 b/tests/day8/1.1
new file mode 100644
index 0000000..0cfbf08
--- /dev/null
+++ b/tests/day8/1.1
@@ -0,0 +1 @@
+2
diff --git a/tests/day8/2 b/tests/day8/2
new file mode 100644
index 0000000..7d1b58d
--- /dev/null
+++ b/tests/day8/2
@@ -0,0 +1,5 @@
+LLR
+
+AAA = (BBB, BBB)
+BBB = (AAA, ZZZ)
+ZZZ = (ZZZ, ZZZ)
diff --git a/tests/day8/2.1 b/tests/day8/2.1
new file mode 100644
index 0000000..1e8b314
--- /dev/null
+++ b/tests/day8/2.1
@@ -0,0 +1 @@
+6
diff --git a/tests/day8/3 b/tests/day8/3
new file mode 100644
index 0000000..5b3fa58
--- /dev/null
+++ b/tests/day8/3
@@ -0,0 +1,10 @@
+LR
+
+11A = (11B, XXX)
+11B = (XXX, 11Z)
+11Z = (11B, XXX)
+22A = (22B, XXX)
+22B = (22C, 22C)
+22C = (22Z, 22Z)
+22Z = (22B, 22B)
+XXX = (XXX, XXX)
diff --git a/tests/day8/3.2 b/tests/day8/3.2
new file mode 100644
index 0000000..1e8b314
--- /dev/null
+++ b/tests/day8/3.2
@@ -0,0 +1 @@
+6