In computer science, a substring index is a data structure which gives substring search in a text or text collection in sublinear time. If you have a document of length , or a set of documents of total length , you can locate all occurrences of a pattern in time. (See Big O notation.) The phrase full-text index is also often used for an index of all substrings of a text. But is ambiguous, as it is also used for regular word indexes such as inverted files and document retrieval. See full text search. Substring indexes include: Suffix tree Suffix array N-gram index, an inverted file for all N-grams of the text Compressed suffix array FM-index LZ-index References Algorithms on strings String data structures Database index techniques