Shopify·Machine Learning Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say

May 2026Remote

Summary

Shopify ML engineer screen, pretty standard coding problem but the follow-ups about obstacles and path tracking added some pressure toward the end. Nothing too wild but I left feeling like I could've been cleaner on the edge cases.

Questions Asked (1)

Given an m x n grid and a robot starting at position (r, c), process a string of movement commands ('U', 'D', 'L', 'R') and return the robot's final position. Any move that would take the robot out of bounds should be ignored.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

Seemed easy at first and I think I got a bit overconfident.

Create a free account to read the full note

AI HintsAI Generated

Suggested Approach

Clarify the problem constraints (grid size, starting position, command string) and confirm edge cases like empty commands or starting out of bounds. Then describe a straightforward simulation: iterate through each command, compute the candidate new position, and update only if it stays within bounds. Finally, discuss time and space complexity and potential optimizations or trade-offs.

Pro tip: Mention that you would validate the starting position and handle empty command strings gracefully, showing attention to edge cases that often trip up candidates. Also, briefly note that the simulation is O(n) time and O(1) space, which is optimal for this problem.

1. Clarify requirements and constraints

Ask about grid dimensions, starting position validity, command string length, and whether moves are case-sensitive. Confirm the expected output format (e.g., tuple, list, or coordinates).

2. Outline the simulation approach

Explain that you will iterate through each command, compute the new position, and check bounds before updating. Emphasize that out-of-bounds moves are ignored.

3. Handle edge cases

Discuss scenarios like empty command string, starting position on the boundary, and invalid starting position. Mention how you would handle them (e.g., return starting position if no moves).

4. Analyze complexity and trade-offs

State that time complexity is O(n) where n is the number of commands, and space complexity is O(1). Compare with alternative approaches if any (e.g., precomputing boundaries).

5. Write clean, testable code

Describe how you would implement the solution with clear variable names and modular checks. Mention testing with sample inputs and edge cases.

Key Points to Mention

Boundary checking before updating position to ignore invalid moves
Time and space complexity analysis (O(n) time, O(1) space)
Edge cases: empty command string, starting position at boundary, invalid start
Use of a direction mapping (e.g., dictionary) for clarity and maintainability
Potential for early termination if no commands or if grid is 1x1
Testing strategy: unit tests for each direction and boundary conditions

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