Day 6 part 2 Ruby solution

Author: creideiki

06-2.rb

@@ -0,0 +1,154 @@
+#!/usr/bin/env ruby
+
+require 'numo/narray'
+require 'parallel'
+
+class Map
+  attr_reader :height, :width, :map, :init_guard_x, :init_guard_y, :init_guard_dir
+
+  def initialize(input)
+    @height = input.size
+    @width = input[0].size
+    @map = Numo::UInt8.zeros(@height, @width)
+    @height.times do |y|
+      @width.times do |x|
+        case input[y][x]
+        when '.'
+          @map[y, x] = 0
+        when '#'
+          @map[y, x] = 1
+        when '^'
+          @map[y, x] = 2
+          @init_guard_y = @guard_y = y
+          @init_guard_x = @guard_x = x
+          @init_guard_dir = @guard_dir = :north
+        end
+      end
+    end
+  end
+
+  def initialize_copy(other)
+    @height = other.height
+    @width = other.width
+    @map = other.map.clone
+    @init_guard_x = @guard_x = other.init_guard_x
+    @init_guard_y = @guard_y = other.init_guard_y
+    @init_guard_dir = @guard_dir = other.init_guard_dir
+  end
+
+  def reset!
+    @guard_y = @init_guard_y
+    @guard_x = @init_guard_x
+    @guard_dir = @init_guard_dir
+  end
+
+  def add_obstacle(y, x)
+    @map[y, x] = 1
+  end
+
+  def walk!
+    visited = []
+
+    res = :again
+    while res == :again
+      case @guard_dir
+      when :north
+        dy = -1
+        dx = 0
+      when :east
+        dy = 0
+        dx = 1
+      when :south
+        dy = 1
+        dx = 0
+      when :west
+        dy = 0
+        dx = -1
+      end
+
+      next_x = @guard_x + dx
+      next_y = @guard_y + dy
+
+      if visited.include? [@guard_y, @guard_x, @guard_dir]
+        res = :loop
+        break
+      end
+
+      visited << [@guard_y, @guard_x, @guard_dir]
+
+      if next_x < 0 or next_x >= @width or
+         next_y < 0 or next_y >= @height
+        @guard_x = next_x
+        @guard_y = next_y
+        res = :leave
+      elsif @map[next_y, next_x] == 1
+        @guard_dir = case @guard_dir
+                     when :north
+                       :east
+                     when :east
+                       :south
+                     when :south
+                       :west
+                     when :west
+                       :north
+                     end
+        res = :again
+      else
+        @map[next_y, next_x] = 2
+        @guard_x = next_x
+        @guard_y = next_y
+        res = :again
+      end
+    end
+
+    if res == :loop
+      1
+    elsif res == :leave
+      0
+    end
+  end
+
+  def route
+    route = []
+    @height.times do |y|
+      @width.times do |x|
+        route << [y, x] if @map[y, x] == 2
+      end
+    end
+    route
+  end
+
+  def inspect
+    to_s
+  end
+
+  def to_s
+    s  = "<#{self.class}:\n"
+    s += "Guard: (#{@guard_y}, #{@guard_x}) #{@guard_dir}\n"
+    @height.times do |y|
+      @width.times do |x|
+        s += case @map[y, x]
+             when 0
+               '.'
+             when 1
+               '#'
+             when 2
+               'X'
+             end
+      end
+      s += "\n"
+    end
+    s += ">"
+    s
+  end
+end
+
+map = Map.new File.read('06.input').lines.map(&:strip)
+map.walk!
+
+puts(Parallel.map(map.route) do |candidate_obstacle|
+  simulation = map.clone
+  simulation.reset!
+  simulation.add_obstacle(candidate_obstacle[0], candidate_obstacle[1])
+  simulation.walk!
+end.sum)