Counting closed trails

  • Authors:
  • Andreas BjöRklund;Petteri Kaski

  • Affiliations:
  • Department of Computer Science, Lund University, P.O. Box 118, 22100 Lund, Sweden;Helsinki Institute for Information Technology HIIT & Department of Information and Computer Science, Aalto University, P.O. Box 15400, FI-00076 Aalto, Finland

  • Venue:
  • Information Processing Letters
  • Year:
  • 2013

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Abstract

A closed trail is a connected graph whose every vertex is incident to an even number of edges. We give a deterministic algorithm that in time 2^m^/^2poly(m,n) finds the number of closed trails in a given graph G with n vertices and m edges. Moreover, within the same time bound we can determine every possible vertex set of a closed trail in G, together with the associated number of closed trails. Our algorithm can be used to deterministically find the longest cycle in an n-vertex claw-free graph in time 2^n^/^2poly(m,n) via a framework presented by Broersma et al. (in press, http://dx.doi.org/10.1007/s00453-011-9576-4) [5], thus improving both upon the O(1.66^n) time randomized algorithm for general graphs (Bjorklund, 2010, http://dx.doi.org/10.1109/FOCS.2010.24, [1]), as well as the O(1.69^n) time deterministic algorithm for claw-free graphs by Broersma et al.