Improved Compact Visibility Representation of Planar Graph via Schnyder's Realizer

  • Authors:

  • Ching-Chi Lin;Hsueh-I Lu;I.-Fan Sun

  • Affiliations:

  • -;-;-

  • Venue:
  • STACS '03 Proceedings of the 20th Annual Symposium on Theoretical Aspects of Computer Science
  • Year:
  • 2003

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Abstract

Let G be an n-node planar graph. In a visibility representation of G, each node of G is represented by a horizontal segment such that the segments representing any two adjacent nodes of G are vertically visible to each other. In this paper, we give the best known compact visibility representation of G. Given a canonical ordering of the triangulated G, our algorithm draws the graph incrementally in a greedy manner. We show that one of three canonical orderings obtained from Schnyder's realizer for the triangulated G yields a visibility representation of G no wider than 驴22n-42/15驴. Our easy-to-implement O(n)-time algorithm bypasses the complicated subroutines for four-connected components and four-block trees required by the best previously known algorithm of Kant. Our result provides a negative answer to Kant's open question about whether 驴3n-6/2驴 is a worst-case lower bound on the required width. Moreover, if G has no degree-5 node, then our output for G is no wider than 驴4n-7/3驴. Also, if G is four-connected, then our output for G is no wider than n-1, matching the best known result of Kant and He. As a by-product, we obtain a much simpler proof for a corollary of Wagner's Theorem on realizers, due to Bonichon, Sa毛c, and Mosbah.