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CRDTs vs OT, presence, cursor broadcasting, and conflict-free merging when 50 people edit the same doc at once.
Design a collaborative editor where multiple users see each other's edits in real time, without conflicts, without losing work, and without a central lock. Users can be on flaky networks, can go offline mid-edit, can rejoin hours later, and the system must merge their work coherently.
This is the canonical "no easy answer" system design problem. It forces a candidate to pick between two famously hard families - operational transformation (OT) and conflict-free replicated data types (CRDTs) - and defend the choice. Strong candidates explain why a naive last-write-wins approach loses data and walk through a concrete merge example.
Asking these before diving into a solution is the difference between a "hire" and a "no signal" rating. Pick the questions whose answers would change your design.
Capacity estimation · architecture with all 8 components explained · 6 deep dives · trade-off analysis · 8 common follow-up questions
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Reading is the floor. The interview signal is in walking through this live with someone probing follow-ups. Use the AI mock interview to practice talking through requirements, architecture, and trade-offs out loud.
Mock interview: design Real-Time Collab →