Marsbot Challenge

This project is an implementation of the classic Martian Robots coding challenge. Robots move on a rectangular grid, following sequences of instructions. If a robot leaves the grid, it is marked as LOST and leaves a scent that prevents later robots from repeating the same mistake.

Tech Choices

• Language: C# was chosen for its strong typing, performance, and suitability for console applications.
• Structure: The solution is split into clear classes for grid, robot, position, and direction to keep logic organized and maintainable.
• Extension Methods: Used for direction logic to keep code modular and readable.
• No UI: The program is a console app, focused only on the requirements for simplicity and clarity.

Problem Approach

• The grid is modeled as a class that tracks boundaries and scent positions where robots are lost.
• Robots are simulated step-by-step, following instructions and updating their position and orientation.
• Scent logic prevents robots from getting lost at the same spot as previous robots.
• Input is parsed from the console or file, supporting flexible usage and easy testing.

Project Structure

• Program.cs — Entry point, handles input, validation, and simulation loop.
• Robot.cs — Robot logic (turning, moving, lost state).
• Grid.cs — Grid boundaries and scent tracking.
• Position.cs — Struct representing coordinates.
• Direction.cs — Enum and extensions for turning/moving directions.

Requirements

• .NET 7 SDK or later installed.
• A text file with input instructions (e.g. instructions.txt).

Input Format

The input consists of:

1. Upper-right coordinates of the grid.

2. Pairs of lines for each robot:

   • Starting position and orientation.
   • Instruction string.

Example:

5 3
1 1 E
RFRFRFRF
3 2 N
FRRFLLFFRRFLL
0 3 W
LLFFFLFLFL

Output Format

One line per robot with its final coordinates and orientation. Append LOST if the robot fell off the grid.

Example output:

1 1 E
3 3 N LOST
2 3 S

Running the Program

Option 1: Using instructions.txt

• Place an instructions.txt file in the build output directory (next to the executable).
• Run the program without arguments:

dotnet run

• The program will:

  • Wait for input from the console. If you press Enter on a blank line, it will load instructions.txt automatically.

Option 2: Redirecting input (recommended for testing)

You can feed a file directly via stdin redirection:

dotnet run < input.txt

Option 3: Manual input

Run the program and paste input directly, then press Enter on a blank line to process it.

Testing

1. Create an input.txt file with the test case.

2. Run:

   dotnet run < input.txt > actual.txt

3. Compare actual.txt against your expected output.

Releases (Prebuilt Binary)

If you prefer not to build from source, download the latest prebuilt binary from the repository’s Releases page and run it directly.

How to use the release:

1. Download the archive from Releases.

2. Unzip.

3. Prepare an input.txt with your test case (see Input Format above), or place an instructions.txt next to the executable for fallback. There is a default instructionx.txt already there which you can modify for updating the instructions. Or can manually enter the instructions when prompted.

4. Run:

   marsbot.exe < input.txt

   or

   marsbot.exe < input.txt >output.txt

or

marsbot.exe

which will prompts for input or fallback into instructions.txt if no input