The nearest colored node in a tree

Paweł Gawrychowski, Gad M. Landau, Shay Mozes, Oren Weimann

Research output: Contribution to journalArticlepeer-review

Abstract

We start a systematic study of data structures for the nearest colored node problem on trees. Given a tree with colored nodes and weighted edges, we want to answer queries (v,c) asking for the nearest node to node v that has color c. This is a natural generalization of the well-known nearest marked ancestor problem. We give an O(n)-space O(log⁡log⁡n)-query solution and show that this is optimal. We also consider the dynamic case where updates can change a node's color and show that in O(n) space we can support both updates and queries in O(log⁡n) time. We complement this by showing that O(polylogn) update time implies Ω(log⁡n/log⁡log⁡n) query time. Finally, we consider the case where updates can change the edges of the tree (link-cut operations). There is a known (top-tree based) solution that requires update time that is roughly linear in the number of colors. We show that this solution is probably optimal by showing that a strictly sublinear update time implies a strictly subcubic time algorithm for the classical all pairs shortest paths problem on a general graph. We also consider versions where the tree is rooted, and the query asks for the nearest ancestor/descendant of node v that has color c, and present efficient data structures for both variants in the static and the dynamic setting.

Original languageEnglish
Pages (from-to)66-73
Number of pages8
JournalTheoretical Computer Science
Volume710
DOIs
StatePublished - 1 Feb 2018

Bibliographical note

Funding Information:
Partially supported by ISF grant 571/14 and BSF grant 2014028.

Publisher Copyright:
© 2017 Elsevier B.V.

Keywords

  • Marked ancestor
  • Nearest colored descendant
  • Top-trees
  • Vertex-label distance oracles

ASJC Scopus subject areas

  • Theoretical Computer Science
  • Computer Science (all)

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