From fcbf4aa68384afbb026003ec3332189282d40bf1 Mon Sep 17 00:00:00 2001
From: Adam Millerchip <adam@millerchip.net>
Date: Fri, 6 Dec 2024 18:22:22 +0900
Subject: [PATCH] Refactor Day6 part 1 to use a struct (will re-use in part 2)

---
 2024/day6.exs | 58 +++++++++++++++++++++++++++++----------------------
 1 file changed, 33 insertions(+), 25 deletions(-)

diff --git a/2024/day6.exs b/2024/day6.exs
index 8008426..68d378a 100755
--- a/2024/day6.exs
+++ b/2024/day6.exs
@@ -1,24 +1,30 @@
 #!/usr/bin/env elixir
+defmodule Patrol do
+  defstruct obstacles: MapSet.new(),
+            visited: MapSet.new(),
+            x: 0,
+            y: 0,
+            max_x: nil,
+            max_y: nil,
+            dir_x: 0,
+            dir_y: -1
+end
+
 defmodule Day6 do
-  def part1({max_x, max_y, {x, y}, obstacles}) do
-    walk(x, y, max_x, max_y, obstacles, MapSet.new(), 0, -1)
-    |> MapSet.size()
+  def part1(%Patrol{} = patrol) when patrol.x == patrol.max_x or patrol.y == patrol.max_y do
+    MapSet.size(patrol.visited)
   end
 
-  def walk(x, y, max_x, max_y, _obstacles, visited, _x_dir, _) when x == max_x or y == max_y do
-    visited
-  end
+  def part1(%Patrol{} = patrol) do
+    next_x = patrol.x + patrol.dir_x
+    next_y = patrol.y + patrol.dir_y
 
-  def walk(x, y, max_x, max_y, obstacles, visited, x_dir, y_dir) do
-    next_x = x + x_dir
-    next_y = y + y_dir
-
-    if MapSet.member?(obstacles, {next_x, next_y}) do
-      {x_dir, y_dir} = turn_right(x_dir, y_dir)
-      walk(x, y, max_x, max_y, obstacles, visited, x_dir, y_dir)
+    if MapSet.member?(patrol.obstacles, {next_x, next_y}) do
+      {dir_x, dir_y} = turn_right(patrol.dir_x, patrol.dir_y)
+      part1(%Patrol{patrol | dir_x: dir_x, dir_y: dir_y})
     else
-      visited = MapSet.put(visited, {x, y})
-      walk(next_x, next_y, max_x, max_y, obstacles, visited, x_dir, y_dir)
+      visited = MapSet.put(patrol.visited, {patrol.x, patrol.y})
+      part1(%Patrol{patrol | x: next_x, y: next_y, visited: visited})
     end
   end
 
@@ -35,16 +41,18 @@ defmodule Day6 do
   def input do
     with [input_filename] <- System.argv(),
          {:ok, input} <- File.read(input_filename) do
-      for <<char::binary-1 <- input>>, reduce: {0, 0, 0, nil, MapSet.new()} do
-        {x, max_x, y, guard, obstacles} ->
-          case char do
-            "." -> {x + 1, max_x, y, guard, obstacles}
-            "#" -> {x + 1, max_x, y, guard, MapSet.put(obstacles, {x, y})}
-            "^" -> {x + 1, max_x, y, {x, y}, obstacles}
-            "\n" -> {0, x, y + 1, guard, obstacles}
-          end
-      end
-      |> Tuple.delete_at(0)
+      {_x, max_x, max_y, {x, y}, obstacles} =
+        for <<char::binary-1 <- input>>, reduce: {0, 0, 0, nil, MapSet.new()} do
+          {x, max_x, y, guard, obstacles} ->
+            case char do
+              "." -> {x + 1, max_x, y, guard, obstacles}
+              "#" -> {x + 1, max_x, y, guard, MapSet.put(obstacles, {x, y})}
+              "^" -> {x + 1, max_x, y, {x, y}, obstacles}
+              "\n" -> {0, x, y + 1, guard, obstacles}
+            end
+        end
+
+      %Patrol{x: x, y: y, max_x: max_x, max_y: max_y, obstacles: obstacles}
     else
       _ -> :error
     end