NP-completeness of st-orientations for plane graphs

  • Authors:
  • Sadish Sadasivam;Huaming Zhang

  • Affiliations:
  • Computer Science Department, University of Alabama in Huntsville, Huntsville, AL;Computer Science Department, University of Alabama in Huntsville, Huntsville, AL

  • Venue:
  • FCT'09 Proceedings of the 17th international conference on Fundamentals of computation theory
  • Year:
  • 2009

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Abstract

An st-orientation or bipolar orientation of a 2-connected graph G is an orientation of its edges to generate a directed acyclic graph with a single source s and a single sink t. Given a plane graph G and two vertices s and t on the exterior face of G, the problem of finding an optimum st-orientation, i.e., an st-orientation in which the length of the longest st-path is minimized, was first proposed indirectly by Rosenstiehl and Tarjan in [14] and then later directly by He and Kao in [6]. In this paper, we prove that, given a 2-connected plane graph G, two vertices s, t, on the exterior face of G and a positive integer K, the decision problem of whether G has an st-orientation, where the maximum length of an st-path is ≤ K, is NP-Complete. This solves a long standing open problem on the complexity of optimum st-orientations for plane graphs.