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Design a robot movement command system | Shopify Interview Question

Q: Design a robot movement command system

This question evaluates design and implementation skills for an extensible, command-driven robot movement system, covering state representation on a 2D integer grid, directional updates, command dispatching, input/output semantics, and explicit handling policies for invalid commands.

Robot Movement (Pair Programming)

You are given an empty starter repository (only a README). Implement a small, testable robot movement module that can:

Represent a robot on a 2D grid.
Receive a sequence of user commands.
Execute those commands to update the robot’s position and direction.
Be easily extensible as new valid commands are added over time.

Requirements

Robot state
- The robot has a position (x, y) on an integer grid.
- The robot has a facing direction: one of {N, E, S, W} .
Commands (initial set) Support at least these commands:
- L : rotate 90° left (N→W→S→E→N)
- R : rotate 90° right (N→E→S→W→N)
- F : move forward by 1 step in the direction it is currently facing
Input / Output
- Input: initial state (x0, y0, dir0) and a command string like "FFLFFR" (or an equivalent list/array of commands).
- Output: final state (x, y, dir) after executing all commands.
Invalid command handling
- Define and implement a clear policy for unknown commands (e.g., throw an error, ignore, or collect errors). State your choice.
Extensibility constraint (core design requirement)
- Assume valid commands will keep expanding (e.g., B for backward, J for jump, U for undo, etc.).
- Design the command system so adding a new command does not require rewriting large parts of the robot execution logic.
- Discuss/implement a command abstraction (e.g., command objects, a registry/dispatcher, etc.).
Testing
- Write small, incremental tests as you implement.
- After finishing, explain:
  - What else you would optimize.
  - How you would do systematic testing (unit tests, property-based tests, edge cases).

Example

Initial: (0, 0, N)
Commands: "FFRFF"
Expected final: (2, 2, E)

Constraints (you may assume)

Command string length: up to ~10^5.
Grid is unbounded (no walls/obstacles) unless you explicitly choose to add bounds as an extension.

Implement the core classes/functions (e.g., Robot, command execution/dispatcher) and demonstrate with tests.

Robot Movement (Pair Programming)

You are given an empty starter repository (only a README). Implement a small, testable robot movement module that can:

Represent a robot on a 2D grid.
Receive a sequence of user commands.
Execute those commands to update the robot’s position and direction.
Be easily extensible as new valid commands are added over time.

Requirements

Robot state
- The robot has a position (x, y) on an integer grid.
- The robot has a facing direction: one of {N, E, S, W} .
Commands (initial set) Support at least these commands:
- L : rotate 90° left (N→W→S→E→N)
- R : rotate 90° right (N→E→S→W→N)
- F : move forward by 1 step in the direction it is currently facing
Input / Output
- Input: initial state (x0, y0, dir0) and a command string like "FFLFFR" (or an equivalent list/array of commands).
- Output: final state (x, y, dir) after executing all commands.
Invalid command handling
- Define and implement a clear policy for unknown commands (e.g., throw an error, ignore, or collect errors). State your choice.
Extensibility constraint (core design requirement)
- Assume valid commands will keep expanding (e.g., B for backward, J for jump, U for undo, etc.).
- Design the command system so adding a new command does not require rewriting large parts of the robot execution logic.
- Discuss/implement a command abstraction (e.g., command objects, a registry/dispatcher, etc.).
Testing
- Write small, incremental tests as you implement.
- After finishing, explain:
  - What else you would optimize.
  - How you would do systematic testing (unit tests, property-based tests, edge cases).

Example

Initial: (0, 0, N)
Commands: "FFRFF"
Expected final: (2, 2, E)

Constraints (you may assume)

Command string length: up to ~10^5.
Grid is unbounded (no walls/obstacles) unless you explicitly choose to add bounds as an extension.

Implement the core classes/functions (e.g., Robot, command execution/dispatcher) and demonstrate with tests.

Design a robot movement command system

Quick Overview

Robot Movement (Pair Programming)

Requirements

Example

Constraints (you may assume)

Comments (0)

Design a robot movement command system

Quick Overview

Robot Movement (Pair Programming)

Requirements

Example

Constraints (you may assume)

Comments (0)