MARS Rover Exercise in C#

The Mars Rover simulation is one of the most popular tests spreaded by companies wich want to screen candidates with a pratical test. Here’s the requirements:

” The problem specified below requires a solution that receives input, does some processing and then returns some output. You are free to implement any mechanism for feeding input into your solution. You should provide sufficient evidence that your solution is complete by, as a minimum, indicating that it works correctly against the supplied test data. Using a unit testing framework would satisfy these requirements.
Specification

A squad of robotic rovers are to be landed by NASA on a plateau on Mars. This plateau, which is curiously rectangular, must be navigated by the rovers so that their on board cameras can get a complete view of the surrounding terrain to send back to Earth. A rover’s position is represented by a combination of an x and y co-ordinates and a letter presenting one of the four cardinal compass points. The plateau is divided up into a grid to simplify navigation. An example position might be 0, 0, N, which means the rover is in the bottom
left corner and facing North.

In order to control a rover, NASA sends a simple string of letters. The possible letters are ‘L’, ‘R’ and ‘M’. ‘L’ and ‘R’ makes the rover spin 90 degrees left or right respectively, without moving from its current spot. ‘M’ means move forward one grid point, and maintain the same heading.

Assume that the square directly North from (x, y) is (x, y+1).

Input:

The first line of input is the upper-right coordinates of the plateau, the lower-left coordinates are assumed to be 0,0.  The rest of the input is information pertaining to the rovers that have been deployed. Each rover has two lines of input. The first line gives the rover’s position, and the second line is a series of instructions telling the rover how to explore the plateau. The position is made up of two integers and a letter separated by spaces, corresponding to the x and y co-ordinates and the rover’s orientation.  Each rover will be finished sequentially, which means that the second rover won’t start to move until the first one has finished moving.

Output:

The output for each rover should be its final co-ordinates and heading.

Test Input:
55
12N
LMLMLMLMM
33E
MMRMMRMRRM

Expected Output:
13N
51E    “

The conplete solution, including unit tests, can be downloaded here.

Here is the key part of the application, having an enum representing the cardinal points N E S W with corresponding values of 1 2 3 4

public enum Orientations
{
   [Utils.StringValueAttribute("N")]
   N = 1,
   [Utils.StringValueAttribute("E")]
   E = 2,
   [Utils.StringValueAttribute("S")]
   S = 3,
   [Utils.StringValueAttribute("W")]
   W = 4
}

This allow us to set the orientation by decreasing/increasing the value of the Orientation property of the robot:

  • If the value is bigger than 3, so to W, the robot orientation is set to N.
  • If the value is smaller than 1, so to N, the robot orientation is set to W.
private void TurnLeft()
{
   RoverOrientation = (RoverOrientation - 1) < Orientations.N ? Orientations.W : RoverOrientation - 1;
}

private void TurnRight()
{
   RoverOrientation = (RoverOrientation + 1) > Orientations.W ? Orientations.N : RoverOrientation + 1;
}

The complete Rover class:

public class Rover : IRover
{
        public IPosition RoverPosition { get; set; }
        public Orientations RoverOrientation { get; set; }
        public IPlateau RoverPlateau { get; set; }

        public Rover(IPosition roverPosition, Orientations roverOrientation, IPlateau roverPlateau)
        {
            RoverPosition = roverPosition;
            RoverOrientation = roverOrientation;
            RoverPlateau = roverPlateau;
        }

        public void Process(string commands)
        {
            foreach (var command in commands)
            {
                switch (command)
                {
                    case ('L'):
                        TurnLeft();
                        break;
                    case ('R'):
                        TurnRight();
                        break;
                    case ('M'):
                        Move();
                        break;
                    default:
                        throw new ArgumentException(string.Format("Invalid value: {0}", command));
                }
            }
        }

        public bool IsRobotInsideBoundaries
        {
            get
            {
                bool isInsideBoundaries = false;
                if (RoverPosition.X > RoverPlateau.PlateauPosition.X || RoverPosition.Y > RoverPlateau.PlateauPosition.Y)
                    isInsideBoundaries = true;
                return isInsideBoundaries;
            }
        }

        private void TurnLeft()
        {
            RoverOrientation = (RoverOrientation - 1) < Orientations.N ? Orientations.W : RoverOrientation - 1;
        }

        private void TurnRight()
        {
            RoverOrientation = (RoverOrientation + 1) > Orientations.W ? Orientations.N : RoverOrientation + 1;
        }

        private void Move()
        {
            if (RoverOrientation == Orientations.N)
            {
                RoverPosition.Y++;
            }
            else if (RoverOrientation == Orientations.E)
            {
                RoverPosition.X++;
            }
            else if (RoverOrientation == Orientations.S)
            {
                RoverPosition.Y--;
            }
            else if (RoverOrientation == Orientations.W)
            {
                RoverPosition.X--;
            }
        }

        public override string ToString()
        {
            string printedRoverPosition = string.Format("{0} {1} {2}", RoverPosition.X, RoverPosition.Y, RoverOrientation.GetStringValue());
            if (IsRobotInsideBoundaries)
                printedRoverPosition =
                    string.Format("Rover outside the plateau, Rover position: {0} , plateau limit {1}",
                                  printedRoverPosition, RoverPlateau.PlateauPosition.ToString());

            return printedRoverPosition;

        }

    }



1 Comment

Great code. Just one small modification I made. Since you went through the trouble of declaring interfaces, it would be better to
change Position object in IPlateau to IPosition PlateauPosition. So the code becomes like.

public interface IPlateau
{
IPosition PlateauPosition { get; }
}

public class Plateau : IPlateau
{
public IPosition PlateauPosition { get; private set;}

public Plateau(IPosition position)
{
PlateauPosition = position;
}
}

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