Evolve Duplicate Detection for Sliding Windows and Read-Heavy Queries
Last updated: September 3, 2026
Quick Overview
The question asks the candidate to design a system for detecting duplicates in a sliding window, focusing on optimizing for read-heavy queries while ensuring efficient updates.
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The question asks the candidate to design a system for detecting duplicates in a sliding window, focusing on optimizing for read-heavy queries while ensuring efficient updates.
This question is often posed during the technical screen round at Google to evaluate a candidate's ability to design scalable systems. Interviewers are looking for a clear understanding of data structures, algorithm efficiency, and optimization techniques, particularly in scenarios where read operations significantly outnumber write operations. Candidates are expected to demonstrate their problem-solving skills and ability to think critically about trade-offs in system design.
What the Interviewer Expects
- Explain the requirements for duplicate detection in a sliding window context.
- Discuss the choice of data structures that allow for efficient querying and updating.
- Provide a high-level design of the solution, including how to handle read-heavy scenarios.
- Address potential trade-offs and scaling considerations.
- Illustrate the solution with examples or pseudocode.
Key Topics to Cover
How to Approach This
- Apply SOLID principles. Single Responsibility makes code testable, Open/Closed makes it extensible.
- Choose data structures based on access patterns, not familiarity.
- Prefer immutable data and message passing over shared mutable state for concurrency.
- Design APIs with RESTful conventions, versioning, meaningful errors, and pagination from day one.
Possible Follow-up Questions
- How would you handle edge cases in your design?
- What changes would you make if the window size were to change dynamically?
- Can you explain how your solution would scale with an increasing number of queries?
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Practice System Design ProblemsSample Answer
Requirements
To design a duplicate detection system for a sliding window, we need to keep track of elements within a specific range while allowing for efficient querying and updating. The system should support con...
High-Level Design
A suitable approach is to use a combination of a hash set and a queue. The hash set will allow for O(1) average time complexity for checking duplicates, while the queue will maintain the order of elem...
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