Exact counting of Euler tours for generalized series-parallel graphs

Prasad Chebolu, Mary Cryan, Russell Martin

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

We give a simple polynomial-time algorithm to exactly count the number of Euler tours (ETs) of any Eulerian generalized series-parallel graph, and show how to adapt this algorithm to exactly sample a random ET of the given generalized series-parallel graph. Note that the class of generalized series-parallel graphs includes all outerplanar graphs. We can perform the counting in time O(mΔ3), where Δ is the maximum degree of the graph with m edges. We use O(mnΔ2logΔ) bits to store intermediate values during our computations. To date, these are the first known polynomial-time algorithms to count or sample ETs of any class of graphs; there are no other known polynomial-time algorithms to even approximately count or sample ETs of any other class of graphs. The problem of counting ETs is known to be #P-complete for general graphs (Brightwell and Winkler, 2005 [2]) also for planar graphs (Creed, 2010 [3]).

Original languageEnglish
Pages (from-to)110-122
Number of pages13
JournalJournal of Discrete Algorithms
Issue numbern/a
Publication statusPublished - Jan 2012

Keywords / Materials (for Non-textual outputs)

  • Euler tour
  • Series-parallel graph


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