Mars Rover Navigation API

A modular Node.js + Express backend API that simulates the navigation of robotic rovers exploring a rectangular plateau on Mars (or the Moon).
The API receives rover positions and navigation commands, processes them sequentially, and returns their final coordinates and orientation.

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Problem

A squad of robotic rovers is deployed on a rectangular plateau. Each rover can move across the grid using navigation commands sent from mission control.

The plateau is divided into a grid where:

• The bottom-left coordinate is (0,0)
• The top-right coordinate defines the plateau boundary

Each rover has:

• an x coordinate
• a y coordinate
• a direction (N, E, S, W)

Example position:

1 2 N

Meaning:

• x = 1
• y = 2
• facing North

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Rover Commands

The rover receives a string of instructions:

Command	Meaning
L	Rotate 90° Left
R	Rotate 90° Right
M	Move forward one grid point

Example:

LMLMLMLMM

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Important Rules

• Rovers move one at a time
• The next rover starts only after the previous rover finishes
• Rovers cannot move outside the plateau
• Invalid commands or out-of-bound movements return errors

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Approach

The solution follows a layered backend architecture to keep responsibilities separated and code maintainable.

The navigation process works as follows:

1. The client sends a request with plateau dimensions and rover data.
2. The API validates the request.
3. Each rover is instantiated as a Rover model object.
4. Commands are processed sequentially.
5. Movement and rotation logic update the rover state.
6. Boundary checks ensure the rover stays within the plateau.
7. The final positions are returned as the API response.

Core Logic

Rotation is handled using a directional array:

[N, E, S, W]

Movement rules:

Direction	Movement
N	y + 1
E	x + 1
S	y - 1
W	x - 1

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Architecture

The project is organized into modular backend layers:

mars-rover-navigation
│
├── server.js
├── routes
│     roverRoutes.js
│
├── controllers
│     roverController.js
│
├── services
│     roverService.js
│
├── models
│     Rover.js
│
└── utils
      directionUtils.js

server.js

Application entry point that starts the Express server and registers routes.

routes

Defines API endpoints and maps them to controllers.

controllers

Handles HTTP requests and responses. Validates input and forwards processing to the service layer.

services

Contains the core business logic for navigating multiple rovers.

models

Defines the Rover class, which manages rover state and movement.

utils

Provides helper utilities such as direction rotation logic.

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System Flow

Client Request
      ↓
Express Server
      ↓
Route
      ↓
Controller
      ↓
Service
      ↓
Rover Model
      ↓
Direction Utils
      ↓
Response

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How to Run

1. Clone the repository

git clone https://github.com/Hariksh/Rover_Problem.git
cd Rover_Problem

2. Install dependencies

npm install

3. Start the server

node server.js

Server will start on:

http://localhost:5001

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API Endpoint

POST /api/navigate-rovers

Processes rover navigation commands and returns their final positions.

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Example Input

{
  "plateau": {
    "width": 5,
    "height": 5
  },
  "rovers": [
    {
      "x": 1,
      "y": 2,
      "direction": "N",
      "commands": "LMLMLMLMM"
    },
    {
      "x": 3,
      "y": 3,
      "direction": "E",
      "commands": "MMRMMRMRRM"
    }
  ]
}

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Example Output

{
  "finalPositions": [
    "1 3 N",
    "5 1 E"
  ]
}

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Error Handling

The API validates inputs and handles common errors.

Status Code	Description
400	Missing or invalid input data
422	Invalid command or rover moves outside plateau
500	Unexpected server error

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Tech Stack

• Node.js
• Express.js
• JavaScript (ES6)
• Modular backend architecture

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Author

Hariksh Suryawanshi
Backend Developer Internship Assignment