RMU Mentoring: Puzzlenode problem #4

RMU_mentoring.rb

#!/usr/bin/ruby
require 'pp'

f = File.open("input.txt", "r")
o = File.open("output.txt", "w+")

cases = f.readlines ''
cases.each do |c|
  kase = c.split("\n").map{|i| i.split('')}
  nl = kase[0]
  r = kase[1]
  sl = kase[2]
  max = r.size - 1
  start_pos = r.index('X')

  #go west
  even = true
  hits_west = 0
  start_pos.downto(0) { |i| 
    if even
      if nl[i] == "|"
        hits_west += 1
      end
      even = false
    else
      if sl[i] == "|"
        hits_west += 1
      end
      even = true
    end
  }
  
  #go east
  even = true
  hits_east = 0
  start_pos.upto(max) { |i| 
    if even
      if nl[i] == "|"
        hits_east += 1
      end
      even = false
    else
      if sl[i] == "|"
        hits_east += 1
      end
      even = true
    end
  }
  
  if hits_west <= hits_east
    o.puts "GO WEST"
  else
    o.puts "GO EAST"
  end
end

robots_vs_lasers_refactored.rb

module RobotSaver
  
  def self.run
    directions = File.open('output_new.txt', 'w+')
    
    full_grid = File.read('input.txt')
    conveyor_layouts = RobotFactory.individual_layouts(full_grid)
    conveyor_layouts.each do |layout|
      factory = RobotFactory.new(layout)
      directions.puts factory.least_harmful_direction
    end
  end
  
end

class RobotFactory
  
  attr_accessor :active_lasers
  def initialize(layout)
    @layout = {
      :north_laser => layout.split("\n").first.strip,
      :conveyor_belt => layout.split("\n")[1].strip,
      :south_laser => layout.split("\n").last.strip
    }
    @robot_position = @layout[:conveyor_belt].index('X')
  end
  
  def west_hits
    active_lasers[0..@robot_position].count("|")
  end
  
  def east_hits
    active_lasers[@robot_position..-1].count("|")
  end
  
  def active_lasers
    @active_lasers = ""
    to_check = @robot_position.even? ? [north, south] : [south, north]
    if @active_lasers.length == 0
      (0..@layout[:conveyor_belt].size - 1).each do |i|
        # i % 2 returns 0 or 1 
        # for even robot starting position the north lasers are on even positions and south lasers are on odd positions
        # this is reversed for odd robot starting positions
        @active_lasers << to_check[i % 2][i]
      end
    end
    @active_lasers
  end
  
  def north
    @layout[:north_laser]
  end
  
  def south
    @layout[:south_laser]
  end
  
  def least_harmful_direction
    west_hits <= east_hits ? "GO WEST" : "GO EAST"
  end
  
  def self.individual_layouts(grid)
    grid.split( "\n\n" )
  end
end

RobotSaver.run

robots_vs_lasers_trick.txt

Robots vs. Lasers Trick:

Create active laser string disregarding north, south or the robots position:
For example: active_lasers = "# | # | # #"
All lasers in this string are of the shooting kind
Then from the robot's position simply count the number of lasers to the east and to the west.

Two possibilities:

1. Robot start position is even:

	0 1 2 3 4 5  potentially active north lasers are on even positions (0, 2, 4)
	# | # # | #
	- - X - - -  <= even start position (pos. 2 becomes pos. 0, both are even)
	0 1 2 3 4 5
	| # # | # |  potentially active south lasers are on odd positions (1, 3, 5) 

Iterate through the length of the conveyor belt by index. While iterating, check north for active lasers on even positions and south for active lasers on odd positions. 

2. Robot start position is odd:

	0 1 2 3 4 5  potentially active north lasers are on odd positions (1, 3, 5)
	# | # # | #
	- - - X - -  <= odd start position (pos 3 becomes pos 0, even and odd are reversed)
	0 1 2 3 4 5
	| # # | # |  potentially active south lasers are on even positions (0, 2, 4) 

Iterate through the length of the conveyor belt by index. While iterating, check north for active lasers on odd positions and south for active lasers on even positions.