2019: Day 17 Part 1

2019/day17/part1.rb

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+# frozen_string_literal: true
+
+require_relative 'intcode'
+
+Cell = Struct.new(:r, :c) do
+  def neighbors
+    [
+      Cell.new(r + 1, c),
+      Cell.new(r - 1, c),
+      Cell.new(r, c + 1),
+      Cell.new(r, c - 1)
+    ]
+  end
+end
+
+class World
+  def initialize
+    @cells = {}
+    @max_r = -1
+    @max_c = -1
+  end
+
+  def set(cell, contents)
+    @cells[cell] = contents
+    @max_r = [@max_r, cell.r].max
+    @max_c = [@max_c, cell.c].max
+  end
+
+  def intersections
+    @cells.keys.select { |cell| intersection? cell }
+  end
+
+  def intersection?(cell)
+    scaffold?(cell) && cell.neighbors.all? { |neighbor| scaffold?(neighbor) }
+  end
+
+  SCAFFOLDS = %i[scaffold robot_up robot_down robot_left robot_right] .freeze
+
+  def scaffold?(cell)
+    SCAFFOLDS.include? @cells[cell]
+  end
+
+  def to_s
+    s = String.new
+    (0..@max_r).each do |r|
+      (0..@max_c).each do |c|
+        s << char(@cells[Cell.new(r, c)])
+      end
+      s << "\n"
+    end
+    s
+  end
+
+  CHAR_TO_CONTENTS = {
+    '#' => :scaffold,
+    '.' => :open,
+    '^' => :robot_up,
+    'v' => :robot_down,
+    '<' => :robot_left,
+    '>' => :robot_right,
+    'x' => :robot_tumbling
+  }.freeze
+
+  CONTENTS_TO_CHAR = {
+    scaffold: '#',
+    open: '.',
+    robot_up: '^',
+    robot_down: 'v',
+    robot_left: '<',
+    robot_right: '>',
+    robot_tumbling: 'x'
+  }.freeze
+
+  def self.parse(text)
+    r = c = 0
+    world = new
+    text.each_char do |char|
+      if char == "\n"
+        r += 1
+        c = 0
+        next
+      end
+      contents = CHAR_TO_CONTENTS.fetch(char)
+      world.set(Cell.new(r, c), contents)
+      c += 1
+    end
+    world
+  end
+
+  private
+
+  def char(contents)
+    CONTENTS_TO_CHAR.fetch(contents)
+  end
+end
+
+class Calibrator
+  def initialize(program)
+    @computer = Intcode::Computer.new(program.as_memory)
+    @world = nil
+  end
+
+  def calibrate
+    text = ''
+    while (i = tick)
+      text += i.chr
+    end
+    @world = World.parse(text)
+    alignment(@world.intersections)
+  end
+
+  def alignment(intersections)
+    intersections.sum do |cell|
+      cell.r * cell.c
+    end
+  end
+
+  def tick
+    @computer.next_output
+  end
+end
+
+program = Intcode.read(File.join(__dir__, 'input'))
+c = Calibrator.new(program)
+puts c.calibrate