From 881cc99bcb05cb368fbc20091bcbb5e344bc57f7 Mon Sep 17 00:00:00 2001
From: Adam Hellberg <sharparam@sharparam.com>
Date: Mon, 16 Dec 2024 07:20:46 +0100
Subject: [PATCH] Add Ruby solution for 2024 day 16

---
 src/2024/16/solve.rb | 77 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 77 insertions(+)
 create mode 100755 src/2024/16/solve.rb

diff --git a/src/2024/16/solve.rb b/src/2024/16/solve.rb
new file mode 100755
index 0000000..c91cf3a
--- /dev/null
+++ b/src/2024/16/solve.rb
@@ -0,0 +1,77 @@
+#!/usr/bin/env ruby
+# frozen_string_literal: true
+
+require 'bundler/setup'
+require 'aoc/point'
+
+Point = AoC::Point2
+
+MAZE = ARGF.readlines.flat_map.with_index { |line, y|
+  line.chomp.chars.map.with_index { |cell, x|
+    [Point[x, y], cell]
+  }
+}.to_h
+
+START = MAZE.find { |p, c| c == ?S }[0]
+GOAL = MAZE.find { |p, c| c == ?E }[0]
+
+DIRS = [
+  Point[1, 0], # Right
+  Point[0, 1], # Down
+  Point[-1, 0], # Left
+  Point[0, -1] # Up
+].freeze
+
+def display(path)
+  $width ||= MAZE.keys.map(&:x).max + 1
+  $height ||= MAZE.keys.map(&:y).max + 1
+  $height.times do |y|
+    $width.times do |x|
+      p = Point[x, y]
+      c = MAZE[p]
+      if c == ?. && path.include?(p)
+        print 'O'
+      else
+        print c
+      end
+    end
+    puts
+  end
+end
+
+def dfs2
+  stack = [[START, Point[1, 0], Set.new, 0, [START, GOAL]]]
+  min_cost = Float::INFINITY
+  pos_mins = Hash.new Float::INFINITY
+  paths = Hash.new { |h, k| h[k] = [] }
+
+  until stack.empty?
+    pos, dir, vis, cost, path = stack.pop
+    next if cost > min_cost
+    next if cost > pos_mins[pos] + 1000
+    if pos == GOAL
+      paths[cost] << path
+      min_cost = cost if cost < min_cost
+      next
+    end
+    pos_mins[pos] = cost if cost < pos_mins[pos]
+    vis.add pos
+    path << pos
+    DIRS.each do |new_dir|
+      new_pos = pos + new_dir
+      if !vis.include?(new_pos) && MAZE[new_pos] != ?#
+        turn_cost = new_dir == dir ? 0 : 1000
+        stack.push [new_pos, new_dir, vis.dup, cost + turn_cost + 1, path.dup]
+      end
+    end
+  end
+
+  [min_cost, Set.new(paths[min_cost].flatten)]
+end
+
+part1, paths = dfs2
+
+# display(paths)
+
+puts part1
+puts paths.size
-- 
2.54.0