Design
Search Autocomplete System
Design a real-time search autocomplete system like Google's suggest — returning top completions for a prefix 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 a focused trie/prefix-search problem at scale — interviewers check whether you know how to serve low-latency suggestions from precomputed structures instead of live full-text scans.
02 - Where this system exists in the real world
You interact with this design every day.
Google/Google Maps search-box suggestions
E-commerce product search autocomplete
IDE code-completion suggestion engines
03 - What you'll master
Solve this once. Know it forever.
Use a trie for efficient prefix search
Rank suggestions by frequency/recency
Keep suggestion latency low at scale
04 - What you'll design
7 functional · 4 non-functional requirements.
Return top-5 completions for any typed prefix in < 100ms
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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