Mars Rover Problem Solution

A ruby script written to facilitate the mars rover movement as per movement instructions.

Problem Statement: 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 and location is represented by a combination of x and y co- ordinates and a letter representing 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.

Table of Contents

1. Requirements
2. Setting up the script
   1. From source code
3. Input specifications
4. Usage
   1. Example - Interactive Method
   2. Example - Input json file method
5. Running Tests

Requirements

Ruby: MRI 1.9+ (Tested on Ruby 2.6.3)

Setting up the script

From source code

Clone the repo and cd into "mars_rover_solution" folder. Install all required dependencies as follows $> bundle install

Input specifications

• Plateau grid size to be input as two integers separated by a space.
  • maximum x coordinate - Integer or 0
  • maximum y coordinate - Integer or 0 Example: 5 5
• Rover Start position specification
  • Rover's x coordinate - Integer or 0
  • Rover's y coordinate - Integer or 0
  • Rover's orientation - N, S, E or W To station the rover at position 2 on x axis, 3 on y axis facing north: Use: 2 3 N N represents North, S - South, E - East, W - West
• Rover movement instructions
  • L = Turn Left
  • R = Turn Right
  • M = Move forward Input instructions separated by a space Example: L M R M R R

Usage

Usage: ruby bin/rover_control.rb --interactive
Usage: ruby bin/rover_control.rb --file=/path/to/jsonfile
    -i, --interactive                Run interactively to enter input
    -f, --file=FILE                  Input json file with instructions.
    -h, --help                       Prints this help

Usage: Interactive Method:

Example:

ruby bin/rover_control.rb --interactive
Enter the uppermost right corner coordinates of the plateau grid. (Example input: 7 7):
10 10

Enter the start postion and orientation of the rover you want to control (Example input: 2 2 N):
          OR
Type 'exit' to quit program
3 5 S
Enter instructions to move rover to desired location:
L M R M M
----Position of rover after move is: 4 3 S ----


Enter the start postion and orientation of the rover you want to control (Example input: 2 2 N):
          OR
Enter exit to quit program
exit

The final rover positions are:
4 3 S

Usage: Input json file method

In order to perform bulk rover movements on the grid, one can use the json file method. The convention used is same as explained in the input specifications section. An array of rovers can be passed as shown in the sample file below:

input.json

{
  "grid": {
    "max_x": 5,
    "max_y": 5
  },
  "rovers": [
    {
      "name": "rover1",
      "initial_x": "1",
      "initial_y": "2",
      "orientation": "N",
      "move_instructions": "L M L M L M L M M"
    },
    {
      "name": "rover2",
      "initial_x": "3",
      "initial_y": "3",
      "orientation": "E",
      "move_instructions": "M M R M M R M R R M"
    }
  ]
}

Usage: ruby bin/rover_control.rb --file=input.json

----Position of rover after move is: 1 3 N rover1----

----Position of rover after move is: 5 1 E rover2----


The final rover positions are:
1 3 N rover1
5 1 E rover2

Running Tests

The script comes with test cases that can be run using:

bundle exec rake spec