I started by asking clarifying questions: Should the system support high scalability? What level of availability is expected? Do we need custom aliases? Then, I outlined a basic design using a key-value store to map short URLs to long URLs, discussed how to generate short codes (base62 encoding), and mentioned using a load balancer and cache (like Redis) for performance. I also discussed how to handle collisions, database sharding, and analytics tracking. The interviewer appreciated the attention to trade-offs and scalability concerns.