Design Netflix viewport deduplication
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
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Design an algorithm and the data structures to render the first viewport with no duplicates across all visible rows and columns.
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Describe where the logic runs (client vs. server), how it handles ranking, and runtime complexity.
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Discuss trade-offs, fallbacks, and how you would communicate/iterate with cross-functional teams (recs, product, client, backend).
Constraints & Assumptions
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Preserve the scope, facts, inputs, and requested outputs from the prompt above.
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If the prompt leaves a detail unspecified, state a reasonable assumption before relying on it.
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Keep the answer interview-ready: concise enough to present, but concrete enough to implement or evaluate.
Clarifying Questions to Ask
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Clarify users, core use cases, read/write patterns, scale, latency, availability, and data retention.
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State explicit assumptions before making sizing or architecture decisions.
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Prioritize the functional path first, then address reliability, security, observability, and rollout.
What a Strong Answer Covers
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A scoped requirements summary with concrete non-goals and success metrics.
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API, data model, architecture, consistency, capacity, and operations.
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Reasoned trade-offs among simple and scalable designs, including bottlenecks and failure modes.
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A validation, monitoring, migration, and launch plan appropriate for the risk level.
Follow-up Questions
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What breaks first at 10x traffic or data volume?
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How would you degrade gracefully during dependency failures?
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What metrics and alerts would prove the design is healthy after launch?