Leetcode 642. Design Search Autocomplete System
Design an online autocomplete system that processes characters one-by-one, returning the top 3 historically most frequent sentences that match the current prefix (ranked by frequency, then lexicographically), and inserts new sentences when the special character '#' is entered. The core challenge is supporting fast prefix queries and incremental updates over sentence frequencies, typically requiring a prefix-indexed structure (e.g., trie) or efficient top-k maintenance per prefix.
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