Treewidth Computation and Extremal Combinatorics

  • Authors:
  • Fedor V. Fomin;Yngve Villanger

  • Affiliations:
  • Department of Informatics, University of Bergen, Bergen, Norway N-5020;Department of Informatics, University of Bergen, Bergen, Norway N-5020

  • Venue:
  • ICALP '08 Proceedings of the 35th international colloquium on Automata, Languages and Programming, Part I
  • Year:
  • 2008

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Abstract

For a given graph G and integers b,f≥ 0, let S be a subset of vertices of G ofsize b + 1 such that the subgraph of G induced byS is connected and S can be separated from othervertices of G by removing f vertices. We provethat every graph on n vertices contains at most$n\binom{b+f}{b}$ such vertex subsets. This result from extremalcombinatorics appears to be very useful in the design of severalenumeration and exact algorithms. In particular, we use it toprovide algorithms that for a given n-vertex graphGcompute the treewidth of G in time$\mathcal{O}(1.7549^n)$ by making use of exponential space and intime $\mathcal{O}(2.6151^n)$ and polynomial space;decide in time $\mathcal{O}(({\frac{2n+k+1}{3})^{k+1}\cdotkn^6})$ if the treewidth of G is at most k;list all minimal separators of G in time$\mathcal{O}(1.6181^n)$ and all potential maximal cliques ofG in time $\mathcal{O}(1.7549^n)$.This significantly improves previous algorithms for theseproblems.