Design a robot movement command system
Company: Shopify
Role: Machine Learning Engineer
Category: Coding & Algorithms
Difficulty: easy
Interview Round: Technical Screen
## 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
1. **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}`.
2. **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
3. **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.
4. **Invalid command handling**
- Define and implement a clear policy for unknown commands (e.g., throw an error, ignore, or collect errors). State your choice.
5. **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.).
6. **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.
Overview: 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.
Read the full Shopify Machine Learning Engineer interview experience this question came from
