Solution to Puzzle Node's puzzle #4

readme.md

Robots vs. Lasers

Solution to Puzzle Node's puzzle #4. Execute with

cat input.txt | ruby process.rb > output.txt

process.rb

class Wall
  attr_reader :text
  def initialize(text)
    @text = text
    @lasers = []
    @text.each_char do |c|
      @lasers << (c == '|' ? 1 : 0)
    end
  end

  def hits (position, direction, polarity)
    lasers = direction == :west ?
      @lasers[0..position].reverse :
      @lasers[position..-1]
    lasers = lasers.values_at(* lasers.each_index.select {|e| e.even? ^ (polarity == :odd)}).reduce(0, :+)
  end
end

STDIN.read.split("\n\n").each do |problem|
  lines = problem.split("\n")
  north_wall = Wall.new(lines[0])
  south_wall = Wall.new(lines[2])
  position = lines[1].index('X')

  if north_wall.hits(position, :west, :even) + south_wall.hits(position, :west, :odd) >
     north_wall.hits(position, :east, :even) + south_wall.hits(position, :east, :odd) then
     puts 'GO EAST'
  else
    puts 'GO WEST'
  end
end