Top Tree Compression of Tries

Philip Bille*, Paweł Gawrychowski, Inge Li Gørtz, Gad M. Landau, Oren Weimann

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

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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.

Original languageEnglish
Issue number12
Pages (from-to)3602-3628
Publication statusPublished - 2021


  • Pattern matching
  • Pointer machine
  • Top trees
  • Tree compression


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