The computational complexity of graph contractions I: Polynomially solvable and NP-complete cases

  • Authors:
  • Asaf Levin;Daniel Paulusma;Gerhard J. Woeginger

  • Affiliations:
  • Department of Statistics, The Hebrew University, Jerusalem 91905, Israel;Department of Computer Science, Durham University, Science Laboratories, South Road, Durham DH1 3LE, England;Department of Mathematics and Computer Science, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands

  • Venue:
  • Networks
  • Year:
  • 2008

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Abstract

For a fixed pattern graph H, let H-CONTRACTIBILITY denote the problem of deciding whether a given input graph is contractible to H. This paper is part I of our study on the computational complexity of the H-CONTRACTIBILITY problem. We continue a line of research that was started in 1987 by Brouwer and Veldman, and we determine the computational complexity of the H-CONTRACTIBILITY problem for certain classes of pattern graphs. In particular, we pinpoint the complexity for all graphs H with five vertices except for two graphs, whose polynomial time algorithms are presented in part II. Interestingly, in all connected cases that are known to be polynomially solvable, the pattern graph H has a dominating vertex, whereas in all cases that are known to be NP-complete, the pattern graph H does not have a dominating vertex. © 2007 Wiley Periodicals, Inc. NETWORKS, 2008 An earlier version of this paper appeared in the Proceedings of the 29th International Workshop on Graph-Theoretic Concepts in Computer Science (WG 2003).