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Microsoft·Software Engineer·Onsite - System Design / Architecture·Senior

SeniorPrefer not to say
May 2026

Summary

Microsoft SWE interview that was basically one big system design question about org hierarchies. The problem sounds straightforward until you actually have to think through the update semantics and cycle prevention simultaneously.

Questions Asked (1)

Q1

Design a data structure or service that stores manager-to-report relationships in an organization and supports two operations: querying the total number of people in an employee's reporting chain (all levels down), and updating the hierarchy when someone changes managers. Queries should stay fast, and updates need to handle edge cases like cycles.

System DesignAlgorithms & Data StructuresData Modeling
Author's notes

I went straight to a tree with cached subtree counts per node.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and scale, then propose a graph-based solution with efficient query and update operations. Discuss trade-offs between different data structures and algorithms, and address edge cases like cycles and consistency.

Pro tip: Mention that you would use a topological ordering or maintain subtree sizes with a balanced tree to achieve O(log n) updates and O(1) queries, showing awareness of real-world performance needs.

1. Clarify Requirements

Ask about scale (number of employees, frequency of queries vs updates), consistency requirements, and whether the hierarchy is a tree or can have multiple managers.

2. Choose Data Structure

Propose representing the hierarchy as a directed graph (tree) and discuss options like adjacency lists, parent pointers, or Euler tour trees for efficient subtree size queries.

3. Design Operations

For queries, explain how to compute the total number of reports using subtree sizes. For updates, describe how to detach and reattach nodes while maintaining subtree sizes and detecting cycles.

4. Handle Edge Cases

Address cycle detection (e.g., using visited sets or union-find), root changes, and concurrent updates. Discuss how to ensure atomicity and consistency.

5. Analyze Trade-offs

Compare time and space complexity of your approach with alternatives (e.g., naive traversal vs. augmented trees). Discuss scalability and potential optimizations.

Key Points to Mention

  • Use of subtree sizes to answer queries in O(1) after O(n) preprocessing or O(log n) updates.
  • Cycle detection during updates using DFS or union-find to prevent invalid hierarchies.
  • Trade-offs between query speed and update speed; e.g., caching subtree sizes vs. recomputing on the fly.
  • Handling of multiple roots or disconnected components if the organization has multiple top-level managers.
  • Concurrency control mechanisms like locking or versioning for updates in a distributed setting.
  • Real-world considerations: batch updates, eventual consistency, and persistence.

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