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Competitive Online Search Trees on Trees

Published: 24 June 2023 Publication History

Abstract

We consider the design of adaptive data structures for searching elements of a tree-structured space. We use a natural generalization of the rotation-based online binary search tree model in which the underlying search space is the set of vertices of a tree. This model is based on a simple structure for decomposing graphs, previously known under several names including elimination trees, vertex rankings, and tubings. The model is equivalent to the classical binary search tree model exactly when the underlying tree is a path. We describe an online O(log log n)-competitive search tree data structure in this model, where n is the number of vertices. This matches the best-known competitive ratio of binary search trees. Our method is inspired by Tango trees, an online binary search tree algorithm, but critically needs several new notions including one that we call Steiner-closed search trees, which may be of independent interest. Moreover, our technique is based on a novel use of two levels of decomposition, first from search space to a set of Steiner-closed trees and, second, from these trees into paths.

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Published In

cover image ACM Transactions on Algorithms
ACM Transactions on Algorithms  Volume 19, Issue 3
July 2023
281 pages
ISSN:1549-6325
EISSN:1549-6333
DOI:10.1145/3592471
  • Editor:
  • Edith Cohen
Issue’s Table of Contents

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Association for Computing Machinery

New York, NY, United States

Publication History

Published: 24 June 2023
Online AM: 28 April 2023
Accepted: 23 April 2023
Revised: 09 April 2023
Received: 19 December 2020
Published in TALG Volume 19, Issue 3

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  1. Search trees on trees
  2. tango trees
  3. dynamic optimality

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  • Research-article

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  • European Union’s Horizon 2020
  • NSERC
  • Fonds de la Recherche Scientifique-FNRS
  • NSF AitF
  • Fonds de la Recherche Scientifique-FNRS

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