Design
Typeahead / Instant Search
Design an instant search feature that returns results across multiple entity types (users, products, articles) as the user types.
This is a Low-Level Design (LLD) problem. New to LLD vs HLD? Start here.
01 - Why interviewers ask this
It's the search-engine-scale version of autocomplete — interviewers check if your design survives when the trie itself is too large for one machine.
02 - Where this system exists in the real world
You interact with this design every day.
Search engine query suggestion systems
E-commerce marketplace search-as-you-type
Large-scale product catalog search UIs
03 - What you'll master
Solve this once. Know it forever.
Shard a trie/index across multiple nodes
Aggregate ranked results from multiple shards
Keep suggestion data freshness reasonable
04 - What you'll design
7 functional · 3 non-functional requirements.
Return mixed results (users, products, articles) for any query prefix
6 more requirements inside
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05 - Companies that ask this
You may face this exact question in your next interview.
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