Your question is Autocomplete System Design. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
Design an autocomplete system that suggests words starting with the user's input and updates suggestions based on location, preference, history and trends; then code the solution.
Asked in the System design stage. Covered API design, pagination, rate limiting, caching, mobile bandwidth, ranking, and Trie storage. Reported follow-ups: How do you keep suggestions up to date? How do you handle timezones?