We present a compressed representation of tries based on top tree compression [ICALP 2013] that works on a standard, comparison-based, pointer machine model of computation and supports efficient prefix search queries. Namely, we show how to preprocess a set of strings of total length n over an alphabet of size σ into a compressed data structure of worst-case optimal size O(n/ log σn) that given a pattern string P of length m determines if P is a prefix of one of the strings in time O(min (mlog σ, m+ log n)). We show that this query time is in fact optimal regardless of the size of the data structure. Existing solutions either use Ω (n) space or rely on word RAM techniques, such as tabulation, hashing, address arithmetic, or word-level parallelism, and hence do not work on a pointer machine. Our result is the first solution on a pointer machine that achieves worst-case o(n) space. Along the way, we develop several interesting data structures that work on a pointer machine and are of independent interest. These include an optimal data structures for random access to a grammar-compressed string and an optimal data structure for a variant of the level ancestor problem.
Bibliographical noteFunding Information:
Philip Bille and Inge Li Gørtz: Supported by the Danish Research Council (DFF—4005-00267, DFF—1323-00178). Gad M. Landau: Supported by the Israel Science Foundation Grants 1475/18, and No. 2018141 from the United States-Israel Binational Science Foundation. Oren Weimann: Supported by the Israel Science Foundation Grant 592/17.
© 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.
- Pattern matching
- Pointer machine
- Top trees
- Tree compression