The 60-second answer
Define user objective, inventory scale, freshness, latency, and success/guardrail metrics before architecture. Use multiple candidate generators—collaborative, content, graph, trending, exploration—then a richer ranker with real-time and historical features.
Build the answer in this order
Define user objective, inventory scale, freshness, latency, and success/guardrail metrics before architecture.
Use multiple candidate generators—collaborative, content, graph, trending, exploration—then a richer ranker with real-time and historical features.
Build training labels with exposure-bias awareness, offline feature pipelines consistent with serving, and experimentation/monitoring around the final slate.
Evaluate retrieval recall, ranking NDCG/engagement, diversity/novelty, long-term satisfaction, latency, and negative feedback.
A useful interview mental model
This is the shape of a strong answer—not a script to memorize.
Senior-level signal
- Senior answers cover multi-objective optimization, exploration, feedback loops, and cold-start migration.
- Include feature freshness, fallback tiers, and how to diagnose retrieval vs ranking vs serving failures.
What the interviewer is really testing
Likely follow-up questions
Common weak-answer patterns
- Jumping to a model before defining the product contract.
- Listing components without bottlenecks, metrics, or failure handling.
- Ignoring data quality, serving latency, monitoring, and iteration.