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Google·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
Apr 2026

Summary

Google SWE interview with a system design coding question. Pretty straightforward premise but the details add up fast if you're not careful about your data structure choices.

Questions Asked (1)

Q1

Design a restaurant waitlist system that supports adding a guest, removing a guest by name, and serving the next guest when a table opens up. Implement this as a class or set of functions with complete working code.

Algorithms & Data StructuresSystem Design
Author's notes

My first instinct was to just use a list and call it done, but then the remove-by-name part made me reconsider.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and constraints, then propose a data structure that supports O(1) add, O(1) remove, and O(1) serve-next operations. Implement the solution with a doubly linked list and a hash map, and discuss trade-offs and edge cases.

Pro tip: Mention that you would use a sentinel head and tail to simplify edge cases, and that you would discuss concurrency if the system is multi-threaded. This shows attention to detail and production readiness.

1. Clarify Requirements

Ask about expected operations, constraints (e.g., duplicate names, concurrency), and performance goals. Confirm that add, remove by name, and serve next should be efficient.

2. Choose Data Structures

Propose a doubly linked list to maintain FIFO order and a hash map from name to node for O(1) removal. Explain why this combination meets the requirements.

3. Design the API

Define the class with methods: addGuest(name), removeGuest(name), serveNext(). Specify return values and error handling for missing guests or empty list.

4. Implement and Test

Write clean code with sentinel nodes to avoid null checks. Walk through examples, including edge cases like removing the head or tail, and duplicate names.

5. Analyze and Extend

State time and space complexity: O(1) for all operations, O(n) space. Discuss potential extensions like priority waitlist or concurrency handling.

Key Points to Mention

  • Use a doubly linked list for O(1) insertion and removal, and a hash map for O(1) lookup by name.
  • Sentinel nodes (dummy head and tail) simplify edge cases and avoid null pointer exceptions.
  • Handle duplicate names by either rejecting duplicates or using a unique identifier; clarify with interviewer.
  • Ensure thread safety if the system is concurrent, e.g., using locks or concurrent data structures.
  • Discuss trade-offs: e.g., memory overhead of hash map vs. simplicity of a single list.
  • Consider additional features like notifying guests or estimating wait times, showing product thinking.

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