Theory of Computing Systems

, Volume 55, Issue 1, pp 41–60 | Cite as

String Indexing for Patterns with Wildcards

  • Philip Bille
  • Inge Li Gørtz
  • Hjalte Wedel Vildhøj
  • Søren Vind


We consider the problem of indexing a string t of length n to report the occurrences of a query pattern p containing m characters and j wildcards. Let occ be the number of occurrences of p in t, and σ the size of the alphabet. We obtain the following results.
  • A linear space index with query time O(m+σ j loglogn+occ). This significantly improves the previously best known linear space index by Lam et al. (in Proc. 18th ISAAC, pp. 846–857, [2007]), which requires query time Θ(jn) in the worst case.

  • An index with query time O(m+j+occ) using space \(O(\sigma^{k^{2}} n \log^{k} \log n)\), where k is the maximum number of wildcards allowed in the pattern. This is the first non-trivial bound with this query time.

  • A time-space trade-off, generalizing the index by Cole et al. (in Proc. 36th STOC, pp. 91–100, [2004]).

We also show that these indexes can be generalized to allow variable length gaps in the pattern. Our results are obtained using a novel combination of well-known and new techniques, which could be of independent interest.


String indexing Wildcard Variable length gap Suffix tree LCP data structure 



We thank the anonymous reviewers for their valuable comments. Based on their suggestions we could substantially improve the analysis of the query time for patterns with variable length gaps.


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Copyright information

© Springer Science+Business Media New York 2013

Authors and Affiliations

  • Philip Bille
    • 1
  • Inge Li Gørtz
    • 1
  • Hjalte Wedel Vildhøj
    • 1
  • Søren Vind
    • 1
  1. 1.DTU ComputeTechnical University of DenmarkLyngbyDenmark

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