Localized and compact data-structure for comparability graphs

  • Authors:
  • Fabrice Bazzaro;Cyril Gavoille

  • Affiliations:
  • LaBRI UMR CNRS 5800, Université Bordeaux 1, Talence Cedex, France;LaBRI UMR CNRS 5800, Université Bordeaux 1, Talence Cedex, France

  • Venue:
  • ISAAC'05 Proceedings of the 16th international conference on Algorithms and Computation
  • Year:
  • 2005

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Abstract

We show that every comparability graph of any two-dimensional poset over n elements (a.k.a. permutation graph) can be preprocessed in O(n) time, if two linear extensions of the poset are given, to produce an O(n) space data-structure supporting distance queries in constant time. The data-structure is localized and given as a distance labeling, that is each vertex receives a label of O(log n) bits so that distance queries between any two vertices are answered by inspecting on their labels only. As a byproduct, our data-structure supports all-pair shortest-path queries in O(d) time for distance-d pairs, and so identifies in constant time the first edge along a shortest path between any source and destination. More fundamentally, we show that this optimal space and time data-structure cannot be extended for higher dimension posets (we prove that for comparability graphs of three-dimensional posets, every distance labeling scheme requires Ω(n1/3) bit labels).