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Microsoft·Software Engineer·Onsite - Coding / Algorithms·Intermediate

Intermediate
May 2026

Summary

Microsoft onsite coding round where the actual coding part was fine but I lost a ton of time just figuring out the test setup. The in-memory DB problem wasn't hard, the unfamiliar test framework was.

Questions Asked (1)

Q1

Implement an in-memory database that supports insert, delete by row ID, update, and retrieve operations.

System DesignAPI & IntegrationsTechnical Trade-offs
Author's notes

The actual implementation took maybe 15 minutes, just a dict with some wrapper methods.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and constraints (e.g., data types, concurrency, performance expectations). Then propose a design using a hash map for O(1) row ID lookups and a data structure for efficient range queries if needed. Discuss trade-offs between different data structures and how to handle updates and deletes.

Pro tip: Demonstrate awareness of real-world concerns like thread safety and memory management, and mention how you would test the implementation for correctness and performance.

1. Clarify Requirements

Ask about expected operations, data types, concurrency needs, and performance requirements to scope the problem.

2. Choose Data Structures

Select a hash map for O(1) access by row ID and consider auxiliary structures for ordering or indexing if needed.

3. Define API and Operations

Specify method signatures for insert, delete, update, and retrieve, including parameters and return types.

4. Handle Edge Cases and Concurrency

Address scenarios like duplicate IDs, missing IDs, and thread safety using locks or concurrent data structures.

5. Discuss Trade-offs and Testing

Explain trade-offs between simplicity and performance, and outline a testing strategy for correctness and scalability.

Key Points to Mention

  • Use of hash map for O(1) average-case lookup by row ID
  • Handling of updates and deletes without breaking references
  • Thread safety considerations and synchronization mechanisms
  • Memory management and potential for memory leaks
  • Trade-offs between different data structures (e.g., hash map vs. tree for ordered access)
  • Testing strategies including unit tests and stress tests

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