Max-stretch reduction for tree spanners

K Iwama, Andrzej Lingas, M Okita

    Research output: Chapter in Book/Report/Conference proceedingPaper in conference proceedingResearchpeer-review


    A tree t-spanner T of a graph G is a spanning tree of G whose max-stretch is t, i.e., the distance between any two vertices in T is at most t times their distance in G. If G has a tree t-spanner but not a tree (t - 1)-spanner, then G is said to have max-stretch of t. In this paper, we study the Max-Stretch Reduction Problem: for an unweighted graph G = (V, E), find a set of edges not in E originally whose insertion into G can decrease the max-stretch of G. Our results are as follows: (i) For a ring graph, we give a linear-time algorithm which inserts k edges improving the max-stretch optimally. (ii) For a grid graph, we give a nearly optimal max-stretch reduction algorithm which preserves the structure of the grid. (iii) In the general case, we show that it is NP-hard to decide, for a given graph G and its spanning tree of max-stretch t, whether or not one-edge insertion can decrease the max-stretch to t- 1. (iv) Finally, we show that the max-stretch of an arbitrary graph on n vertices can be reduced to s' >= 2 by inserting O(n/s') edges, which can be determined in linear time, and observe that this number of edges is optimal up to a constant.
    Original languageEnglish
    Title of host publicationAlgorithms and Data Structures / Lecture Notes in Computer Science
    ISBN (Print)978-3-540-28101-6
    Publication statusPublished - 2005
    Event9th International Workshop, WADS 2005 - Waterloo, Canada
    Duration: 2005 Aug 152005 Aug 17

    Publication series

    ISSN (Print)1611-3349
    ISSN (Electronic)0302-9743


    Conference9th International Workshop, WADS 2005

    Subject classification (UKÄ)

    • Computer Science


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