Why a Typeahead Trie Should Store the Top 10 Completions at Every Node

A system design interview question about search autocomplete asks what a service does when a user types a single character. The naive approach of collecting and sorting every query under a prefix's subtree on each keystroke is correct but too slow at scale. Latency limits of about 0.1 seconds, including network time, make precomputation necessary. Illustrative capacity estimates show reads vastly outnumber writes and that client-side debouncing and caching can cut request volume roughly fourfold. The recommended fix is to precompute the top 10 completions at every trie node during build time, so each lookup only walks the prefix and returns a ready list.