mars_rover.rb

#!/usr/bin/ruby

class RoverRemote
  def initialize(cmds)
    parse(cmds)
  end
  
  def parse(cmds)
    cmds.split("\n").each do |cmd|
      case cmd
      when /(\d\s)+[NSEW]/
        @rover = WallE.new(cmd)
      when /[LRM]/
        @rover.do(cmd)
      end
    end
  end
end

class WallE
  def initialize(cmd)
    x, y, @facing = cmd.split(" ")
    @x, @y = x.to_i, y.to_i
  end
  
  def do(cmd)
    cmd.split('').each { |cmd| cmd =~ /M/ ? move : turn(cmd) }
    report
  end
  
  def turn(dir)
    c = %w{ N E S W }
    p = c.index(@facing)
    
    @facing = case dir
    when "L" then c[p-1]
    when "R" then c[p+1] || c[0]
    end
  end
  
  def move
    case @facing
    when "N" then @y+=1
    when "S" then @y-=1
    when "E" then @x+=1
    when "W" then @x-=1
    end
  end
  
  def report
    puts "#{@x} #{@y} #{@facing}"
  end
end

RoverRemote.new("5 5\n1 2 N\nLMLMLMLMM\n3 3 E\nMMRMMRMRRM")