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faire·Software Engineer·Onsite - System Design / Architecture·Intermediate

Intermediate
Jun 2026

Summary

Faire SWE interview that started as a coding problem and then pivoted into a full API design discussion around the same Pascal's Triangle idea. Interesting format, felt more like a design conversation than a standard interview.

Questions Asked (3)

Q1

You've implemented Pascal's Triangle as a coding exercise. Now design the API that a service would expose to clients for retrieving it.

API & IntegrationsSystem DesignTechnical Trade-offs
Author's notes

The pivot from coding to API design threw me a bit.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the requirements: what clients need (e.g., specific rows, ranges, or the whole triangle), expected scale, and performance constraints. Then propose a RESTful API design with clear resource modeling, pagination, caching, and error handling, and discuss trade-offs like precomputation vs. on-demand generation.

Pro tip: Emphasize that the API should abstract away the implementation details (like Pascal's Triangle generation) and focus on providing a stable, versioned contract. Mention that you'd consider rate limiting and authentication for a production service.

1. Clarify Requirements

Ask questions to understand the use case: do clients need individual rows, a range of rows, or the entire triangle? What are the latency and throughput expectations? This shapes the API design.

2. Define Resources and Endpoints

Model the triangle as a resource. For example, GET /triangle/rows/{n} for a specific row, GET /triangle/rows?start={s}&end={e} for a range, and GET /triangle for the whole triangle (with pagination). Use clear, consistent naming.

3. Design Request/Response Formats

Specify JSON responses with fields like rowNumber and values. Include metadata such as totalRows, links for pagination, and error schemas. Consider supporting content negotiation (e.g., JSON, CSV).

4. Address Non-Functional Concerns

Discuss caching (e.g., ETags, Cache-Control), rate limiting, authentication, and versioning. Explain how you'd handle large requests (e.g., max row limit, pagination) and ensure scalability.

5. Discuss Trade-offs and Alternatives

Compare REST vs. GraphQL, precomputation vs. on-demand generation, and synchronous vs. asynchronous processing for large requests. Justify your choices based on the clarified requirements.

Key Points to Mention

  • Resource modeling: treating rows as sub-resources with clear URIs
  • Pagination and limits to prevent abuse and ensure performance
  • Caching strategies (ETags, Cache-Control) for immutable or rarely changing data
  • Error handling with standard HTTP status codes and informative error messages
  • API versioning (e.g., /v1/) to allow future changes without breaking clients
  • Trade-offs between precomputing the triangle (fast reads, high storage) vs. generating on demand (slower reads, low storage)

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

Q2

Should the server handle formatting and rendering of the triangle, or should that be the client's responsibility? Justify your choice.

API & IntegrationsTechnical Trade-offsSystem Design
Author's notes

Said client-side immediately and I think that was right.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the requirements and constraints, then present a balanced trade-off analysis between server-side and client-side rendering. Conclude with a justified recommendation that aligns with the product's needs, such as performance, scalability, and maintainability.

Pro tip: Emphasize that the decision should be driven by the specific use case and non-functional requirements, not dogma. Mention that a hybrid approach or progressive enhancement can often be the best solution.

1. Clarify Requirements

Ask about the expected scale, client capabilities, and performance requirements. Understand if the triangle is static or dynamic, and if there are constraints like offline support or SEO.

2. Evaluate Server-Side Rendering

Discuss pros: consistent rendering, easier caching, reduced client load, and better for SEO. Cons: increased server load, network latency, and less interactivity.

3. Evaluate Client-Side Rendering

Discuss pros: offloads server, enables rich interactivity, and leverages client GPU. Cons: inconsistent across devices, potential performance issues on low-end clients, and SEO challenges.

4. Consider Hybrid Approaches

Mention options like server-side rendering with client-side hydration, or using WebGL on the client with server fallback. Highlight that the choice depends on the specific context.

5. Make a Recommendation

Based on the analysis, recommend one approach and justify it with the requirements. Acknowledge trade-offs and suggest monitoring or iterating if needed.

Key Points to Mention

  • Performance implications: server CPU vs. client GPU, network latency, and scalability.
  • Consistency and reliability: server-side ensures uniform output; client-side may vary by device/browser.
  • Interactivity and user experience: client-side enables real-time updates and smoother interactions.
  • SEO and accessibility: server-side rendering is better for search engines and screen readers.
  • Caching and CDN: server-rendered content can be cached and distributed efficiently.
  • Development and maintenance complexity: client-side may require more complex state management and testing.

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

Q3

How would you handle very large triangle heights, including caching, pagination, and big integer values in the response?

System DesignTechnical Trade-offsAPI & Integrations
Author's notes

This is where I ran out of steam a little.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the problem: what 'triangle heights' means (e.g., computing rows of Pascal's triangle or geometric triangle dimensions) and the scale involved. Then propose a layered solution: use big integers for exact values, cache computed results with an LRU or distributed cache, and paginate API responses to avoid huge payloads. Finally, discuss trade-offs between precision, memory, and latency.

Pro tip: Mention that you would benchmark and profile before optimizing—premature caching or pagination can add complexity without real benefit. Also, consider using a streaming response for extremely large outputs to reduce memory pressure.

1. Clarify requirements and constraints

Ask about the expected range of heights, whether exact values are needed, and the client's ability to handle large responses. This determines if big integers, caching, or pagination are necessary.

2. Choose appropriate data types and algorithms

Use arbitrary-precision integers (e.g., BigInteger in Java, Python's int) for exact values. For geometric triangles, use floating-point with tolerance if exactness isn't critical. Optimize the algorithm to avoid unnecessary recomputation.

3. Implement caching strategy

Cache computed rows or results using an LRU cache for single-node or Redis for distributed systems. Invalidate or evict based on memory limits and access patterns. Consider precomputing common heights.

4. Design pagination for API responses

Paginate large outputs using cursor-based or offset-based pagination. Return only a subset of rows or values per request, with metadata for next/previous pages. Use streaming for very large results if the client supports it.

5. Discuss trade-offs and monitoring

Explain trade-offs: caching improves latency but uses memory; pagination reduces payload but adds round-trips; big integers are exact but slower. Propose monitoring for cache hit rate, response size, and latency.

Key Points to Mention

  • Big integer libraries and their performance characteristics (e.g., BigInteger in Java, Python's int).
  • Caching strategies: LRU, TTL, distributed cache (Redis), and cache invalidation.
  • Pagination techniques: cursor-based vs. offset-based, and when to use streaming.
  • Trade-offs between exactness (big integers) and performance (floating-point).
  • Memory management: avoiding out-of-memory errors with large results.
  • API design considerations: response size limits, compression, and client capabilities.

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