Inverted Index with Phrase Search

Given a list of documents (each document is a whitespace-separated text), build an inverted index and support search. Input documents: List<String> (document id is its index in the list) phrase: String containing one or more space-separated words Output Return a list of matching original document strings (any order) Matching rules If phrase has one word: return all documents containing that word. If phrase has multiple words: return documents containing the phrase with words appearing in order and in consecutive positions. Case-insensitive matching. Constraints D <= 1e4, L <= 1e3, Q <= 20 Example Docs: "the quick brown fox" "the slow brown cow" "to be or not to be that is the question" "bar foo bar barfoo" Queries: "brown" -> docs 1,2 "slow brown" -> doc 2 "the cow" -> doc 2 "bar bar" -> doc 4 Example Input documents=[the quick brown fox; the slow brown cow; to be or not to be that is the question; bar foo bar barfoo] query=brown Output [the quick brown fox, the slow brown cow]