Design a robot movement command system
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.
Shopify
Dec 15, 2025, 12:00 AM
Machine Learning Engineer
Technical Screen
Coding & Algorithms
0
0
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}.
-
The robot has a position
-
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.
-
Input: initial state
-
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.,
Bfor backward,Jfor jump,Ufor 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.).
-
Assume
valid commands will keep expanding
(e.g.,
-
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.