Design a typeahead / autocomplete suggestion system.

Every keystroke has to return ranked suggestions in tens of milliseconds, at search-engine QPS. The interesting part is the data structure and what you precompute, not the query path. Here is the design that holds up under the latency budget.

Updated Sep 2026 · Grounded in real GenAI, LLM, and AI/ML engineering interview loops and written to a senior-engineer editorial bar.