Merge pull request #599 from bu7ch/branch-bu7ch

-PR-#597

Author: t2013anurag

robot_simulator/README.md

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+# Robot Simulator
+
+Write a robot simulator.
+
+A robot factory's test facility needs a program to verify robot movements.
+
+The robots have three possible movements:
+
+- turn right
+- turn left
+- advance
+
+Robots are placed on a hypothetical infinite grid, facing a particular
+direction (north, east, south, or west) at a set of {x,y} coordinates,
+e.g., {3,8}, with coordinates increasing to the north and east.
+
+The robot then receives a number of instructions, at which point the
+testing facility verifies the robot's new position, and in which
+direction it is pointing.
+
+- The letter-string "RAALAL" means:
+  - Turn right
+  - Advance twice
+  - Turn left
+  - Advance once
+  - Turn left yet again
+- Say a robot starts at {7, 3} facing north. Then running this stream
+  of instructions should leave it at {9, 4} facing west.
+
+* * * *
+

robot_simulator/robot_simulator.rb

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+class Robot
+  attr_accessor :x, :y, :bearing
+
+  def at(x, y)
+    self.x = x
+    self.y = y
+  end
+
+  def coordinates
+    [x, y]
+  end
+
+
+  def orient(direction)
+    fail ArgumentError unless cardinal_directions.include?(direction)
+    self.bearing = direction
+  end
+
+  def turn_right
+    turn(:+)
+  end
+
+  def turn_left
+    turn(:-)
+  end
+
+  def advance
+    if bearing == :north
+      self.y += 1
+    elsif bearing == :south
+      self.y -= 1
+    elsif bearing == :west
+      self.x -= 1
+    else
+      self.x += 1
+    end
+  end
+
+ private
+
+   def turn(sign)
+    i = cardinal_directions.index(bearing)
+    self.bearing = cardinal_directions[i.send(sign, 1) % 4]
+  end
+
+  def cardinal_directions
+    [:north, :east, :south, :west]
+  end
+end
+
+class Simulator
+  def instructions(text)
+    text.split('').map { |char| command(char) }
+  end
+
+  def place(robot, position)
+    robot.at(position[:x], position[:y])
+    robot.orient(position[:direction])
+  end
+
+  def evaluate(robot, text)
+    instructions(text).each do |command|
+      robot.send(command)
+    end
+  end
+
+  private
+
+  def command(char)
+    {
+      'R' => :turn_right,
+      'L' => :turn_left,
+      'A' => :advance
+    }[char]
+  end
+
+end