This interview question evaluates requirements, scale assumptions, API/data design, architecture, trade-offs, failure modes, and rollout in a realistic interview setting. A strong answer for Design Netflix viewport deduplication states assumptions, handles edge cases, explains trade-offs, and shows how to validate the result clearly.
##### Question
Design an algorithm and data structures for Netflix home-page viewport rendering so the first screen (all visible rows and columns) contains no duplicate shows. Explain your approach, trade-offs, and communication strategy.
Quick Answer: This interview question evaluates requirements, scale assumptions, API/data design, architecture, trade-offs, failure modes, and rollout in a realistic interview setting. A strong answer for Design Netflix viewport deduplication states assumptions, handles edge cases, explains trade-offs, and shows how to validate the result clearly.
Design an Algorithm to Ensure No Duplicates in the First Netflix Home-Page Viewport
Context
You are rendering a Netflix-style home page composed of multiple horizontal carousels ("rows/rails"). Each row has a ranked list of candidate shows from upstream recommendation sources. On initial render, a user sees the first R_visible rows and the first C tiles per row (the "first screen/viewport").
Requirement: The union of all tiles visible in the first viewport (R_visible × C) must have no duplicate shows (same title), even if rows are sourced independently. Duplicates off-screen are allowed.
Task
Design an algorithm and the data structures to render the first viewport with no duplicates across all visible rows and columns.
Describe where the logic runs (client vs. server), how it handles ranking, and runtime complexity.
Discuss trade-offs, fallbacks, and how you would communicate/iterate with cross-functional teams (recs, product, client, backend).
Clarifying Questions to Ask Guidance
Clarify users, core use cases, read/write patterns, scale, latency, availability, and data retention.
State explicit assumptions before making sizing or architecture decisions.
Prioritize the functional path first, then address reliability, security, observability, and rollout.
What a Strong Answer Covers Guidance
A scoped requirements summary with concrete non-goals and success metrics.
API, data model, architecture, consistency, capacity, and operations.
Reasoned trade-offs among simple and scalable designs, including bottlenecks and failure modes.
A validation, monitoring, migration, and launch plan appropriate for the risk level.
Follow-up Questions Guidance
What breaks first at 10x traffic or data volume?
How would you degrade gracefully during dependency failures?
What metrics and alerts would prove the design is healthy after launch?