The isomorphism problem for k-trees is complete for logspace

  • Authors:
  • V. Arvind;Bireswar Das;Johannes KöBler;Sebastian Kuhnert

  • Affiliations:
  • The Institute of Mathematical Sciences, Chennai 600 113, India;Indian Institute of Technology Gandhinagar, Ahmedabad 382 424, India;Humboldt-Universität, Institut für Informatik, 10099 Berlin, Germany;Humboldt-Universität, Institut für Informatik, 10099 Berlin, Germany

  • Venue:
  • Information and Computation
  • Year:
  • 2012

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Abstract

We show that, for k constant, k-tree isomorphism can be decided in logarithmic space by giving an O(klogn) space canonical labeling algorithm. The algorithm computes a unique tree decomposition, uses colors to fully encode the structure of the original graph in the decomposition tree and invokes Lindell@?s tree canonization algorithm. As a consequence, the isomorphism, the automorphism, as well as the canonization problem for k-trees are all complete for deterministic logspace. Completeness for logspace holds even for simple structural properties of k-trees. We also show that a variant of our canonical labeling algorithm runs in time O((k+1)!n), where n is the number of vertices, yielding the fastest known FPT algorithm for k-tree isomorphism.