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This is a medium difficulty System Design question, commonly asked during Technical Screen rounds at Netflix.

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This question is commonly asked for Software Engineer candidates at Netflix during technical interviews.

Design Netflix viewport deduplication

Last updated: Apr 23, 2026

Quick Overview

This question evaluates algorithmic thinking and data-structure design for deduplication, along with system-design competencies around ranking, client-server trade-offs, and large-scale content rendering.

Netflix

Aug 4, 2025, 10:55 AM

Software Engineer

Technical Screen

System Design

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).

Solution

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