gistfile1.rb

class Array
  def sum
    reduce(:+)
  end
end

def is_laser(character)
  character == '|' ? 1 : 0
end

until ARGF.eof?
  north      = ARGF.gets.chomp.chars
  robot      = ARGF.gets.chomp.index("X")
  south      = ARGF.gets.chomp.chars
  blank_line = ARGF.gets

  puts ["GO WEST","GO WEST","GO EAST"][north.map.with_index { |c,index| (index + robot + 1)%2 * (index <=> robot) * is_laser(c) }.sum +
                                       south.map.with_index { |c,index| (index + robot    )%2 * (index <=> robot) * is_laser(c) }.sum <=> 0]
end