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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 <math>S</math> of length <math>n</math>, or a set of documents <math>D=\{S^1,S^2, \dots, S^d\}</math> of total length <math>n</math>, you can locate all occurrences of a pattern <math>P</math> in <math>o(n)</math> 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 file]]s and [[document retrieval]]. See [[full text search]].

Substring indexes include:

* [[Suffix tree]]
* [[Suffix array]]
* N-gram index, an [[inverted file]] for all [[N-gram]]s of the text
* [[Compressed suffix array]]<ref>R. Grossi and J. S. Vitter, [http://www.di.unipi.it/~grossi/PAPERS/sicomp05.pdf Compressed Suffix Arrays and Suffix Trees, with Applications to Text Indexing and String Matching], ''SIAM Journal on Computing,'' 35(2), 2005, 378-407.</ref>
* [[FM-index]]
* [[LZ-index]]

== References ==
{{reflist}}

[[Category:Algorithms on strings]]
[[Category:String data structures]]
[[Category:Database index techniques]]
[[Category:Substring indices| ]]