2019: Day 11 Part 2

2019/day11/intcode.rb

@@ -137,6 +137,7 @@ module Intcode
         nil
       when 9
         move_relative_base!
+        nil
       when 99
         :done_executing
       else

2019/day11/part2.rb

@@ -0,0 +1,172 @@
+# frozen_string_literal: true
+
+require 'set'
+require_relative 'intcode'
+
+Point = Struct.new(:x, :y) do
+  def to_s
+    "(#{x}, #{y})"
+  end
+end
+
+class Hull
+  def initialize
+    @panels = Hash.new { |hash, key| hash[key] = :black }
+    @painted = Set.new
+  end
+
+  def color_at(point)
+    @panels[point]
+  end
+
+  def paint(point, color)
+    @painted << point
+    @panels[point] = color
+  end
+
+  def painted
+    @painted.count
+  end
+
+  def corners
+    min_x = +Float::INFINITY
+    min_y = +Float::INFINITY
+    max_x = -Float::INFINITY
+    max_y = -Float::INFINITY
+
+    @panels.keys.each do |p|
+      min_x = [min_x, p.x].min
+      min_y = [min_y, p.y].min
+      max_x = [max_x, p.x].max
+      max_y = [max_y, p.y].max
+    end
+
+    upper_left = Point.new(min_x, min_y)
+    lower_right = Point.new(max_x, max_y)
+    [upper_left, lower_right]
+  end
+
+  def to_s
+    tl, br = corners
+
+    s = String.new
+    (tl.y..br.y).each do |y|
+      (tl.x..br.x).each do |x|
+        s << char(color_at(Point.new(x, y)))
+      end
+      s << "\n"
+    end
+    s
+  end
+
+  def char(code)
+    case code
+    when :black
+      ' '
+    when :white
+      # Unicode full block
+      "\u2588"
+    else
+      raise ArgumentError, "unexpected color code: #{code}"
+    end
+  end
+end
+
+class DoneExecuting < StandardError; end
+
+class Robot
+  def initialize(program, hull)
+    @computer = Intcode::Computer.new(program.as_memory) { on_input }
+    @hull = hull
+    @facing = :up
+    @position = Point.new(0, 0)
+  end
+
+  def step
+    color_output = nil
+    direction_output = nil
+
+    color_output = tick until color_output
+    direction_output = tick until direction_output
+
+    @hull.paint(@position, color(color_output))
+    @facing = turn(@facing, direction_output)
+    @position = move(@position, @facing)
+  end
+
+  def tick
+    ret = @computer.tick
+    raise DoneExecuting if ret == :done_executing
+
+    ret
+  end
+
+  def on_input
+    color = @hull.color_at(@position)
+    case color
+    when :black
+      0
+    when :white
+      1
+    else
+      raise ArgumentError, "unexpected color: #{color}"
+    end
+  end
+
+  def color(code)
+    case code
+    when 0
+      :black
+    when 1
+      :white
+    else
+      raise ArgumentError, "unexpected color code: #{code}"
+    end
+  end
+
+  DIRECTIONS = %i[up right down left].freeze
+
+  def turn(facing, direction_code)
+    idx = DIRECTIONS.index(facing)
+    case direction_code
+    when 0
+      # left 90 degrees (ccw)
+      next_idx = (idx - 1) % DIRECTIONS.length
+    when 1
+      # right 90 degrees (cw)
+      next_idx = (idx + 1) % DIRECTIONS.length
+    else
+      raise ArgumentError, "unexpected direction code: #{direction_code}"
+    end
+    DIRECTIONS.fetch(next_idx)
+  end
+
+  def move(pos, direction)
+    case direction
+    when :up
+      Point.new(pos.x, pos.y - 1)
+    when :down
+      Point.new(pos.x, pos.y + 1)
+    when :left
+      Point.new(pos.x - 1, pos.y)
+    when :right
+      Point.new(pos.x + 1, pos.y)
+    else
+      raise ArgumentError, "unexpected direction: #{direction}"
+    end
+  end
+end
+
+hull = Hull.new
+hull.paint(Point.new(0, 0), :white)
+
+program = Intcode.read(File.join(__dir__, 'input'))
+robot = Robot.new(program, hull)
+
+loop do
+  robot.step
+rescue DoneExecuting
+  break
+end
+
+puts hull