k-level crossing minimization is NP-hard for trees

  • Authors:
  • Martin Harrigan;Patrick Healy

  • Affiliations:
  • Complex & Adaptive Systems Laboratory, University College Dublin, Ireland;Dept. of Computer Science & Information Systems, University of Limerick, Ireland

  • Venue:
  • WALCOM'11 Proceedings of the 5th international conference on WALCOM: algorithms and computation
  • Year:
  • 2011

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Abstract

The k-level crossing minimization problem for graphs has received much interest in the graph drawing literature. In this paper we focus on the special case of trees. We show that the 2-level crossing minimization problem for trees where the order of the vertices on one level is fixed is solvable in quadratic time. We also show that the k-level crossing minimization problem for trees for an arbitrary number of levels is NP-Hard. This result exposes a source of difficulty for algorithm designers that compounds earlier results relating to the 2-level crossing minimization problem for graphs.