Shopify·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

Jun 2026

Summary

Shopify coding interview, backend-ish design problem dressed up as a fun Mars rover extension. The base problem was familiar but they layered on multi-rover concurrency management and it got interesting fast.

Questions Asked (1)

You're given a basic Mars rover controller (single rover, starts at origin facing north, supports turn left, turn right, and move). Extend it to support multiple rovers on the same grid simultaneously, with operations to create, delete, and select rovers by ID. Commands like move and turn should apply to whichever rover is currently selected.

System DesignAPI & IntegrationsTechnical Trade-offs

Author's notes

The base rover part I had no problem with, done that one before.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and assumptions, then design a clean object-oriented model with a Rover class and a RoverManager to handle multiple rovers, selection, and command dispatch. Walk through the API design, discuss trade-offs (e.g., data structures for rover storage, error handling), and consider edge cases like invalid IDs or collisions.

Pro tip: Emphasize extensibility and separation of concerns: keep rover state and behavior encapsulated, and make the manager responsible for lifecycle and selection. This shows you think beyond the immediate problem and can design maintainable systems.

1. Clarify Requirements and Assumptions

Ask questions to understand constraints: grid size, collision handling, command syntax, persistence, concurrency, and whether rovers can overlap. State your assumptions clearly.

2. Design the Core Classes

Define a Rover class with position, direction, and methods for move/turn. Create a RoverManager (or Fleet) to store rovers by ID, track the selected rover, and provide create/delete/select operations.

3. Define the API and Command Dispatch

Specify how commands are issued (e.g., a command string or method calls) and how they are routed to the selected rover. Ensure operations like move/turn affect only the selected rover.

4. Handle Edge Cases and Errors

Discuss error handling for invalid IDs, duplicate IDs, deleting the selected rover, or moving out of bounds. Decide on behavior (e.g., throw exceptions, return error codes).

5. Discuss Trade-offs and Extensibility

Compare data structures (e.g., hash map vs list) for rover storage, and consider future extensions like multiple grids, obstacles, or concurrent commands. Mention testing strategy.

Key Points to Mention

Encapsulation: Rover should manage its own state and movement logic.
Selection mechanism: Maintain a reference to the currently selected rover, and ensure commands apply only to it.
Data structure choice: Use a hash map for O(1) rover lookup by ID, and discuss memory vs speed trade-offs.
Error handling: Define clear behavior for invalid operations (e.g., selecting non-existent rover, moving out of bounds).
Extensibility: Design with interfaces or abstract classes to allow future rover types or grid features.
Testing: Suggest unit tests for rover movement, manager operations, and edge cases.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.