NC coloring algorithms for permutation graphs

  • Authors:
  • Maria Andreou;Stavros D. Nikolopoulos

  • Affiliations:
  • University of Patras, Department of Computer Engineering and Informatics, GR-26500 Patras, Greece;University of Ioannina, Department of Computer Science, P.O. Box 1186, GR-45110 Ioannina, Greece

  • Venue:
  • Nordic Journal of Computing
  • Year:
  • 1999

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Abstract

We show that the problem of coloring a permutation graph of size n can be solved in O(log n log k) time using O(kn2/log k log2 n) processors on the CREW PRAM model of computation, where 1 . We estimate the parameter k on random permutation graphs and show that the coloring problem can be solved in O(log n log log n) time in the average-case on the CREW PRAM model of computation with O(n2) processors. Our computational strategy goes as follows: Given a permutation pi; or its corresponding permutation graph G[π], we first construct a directed acyclic graph G*[π] using certain combinatorial properties of π, and then compute longest paths in the directed acyclic graph using divide-and-conquer techniques. We show that the problem of coloring a permutation graph G[π] is equivalent to finding longest paths in its acyclic digraph G*[π]. The best-known parallel algorithms for the same problem run in O(log2 n) time using O(n3/log n) processors on the CREW PRAM model of computation.