Partitioning Graphs into Connected Parts

  • Authors:
  • Pim Hof;Daniël Paulusma;Gerhard J. Woeginger

  • Affiliations:
  • Department of Computer Science, University of Durham, Science Laboratories, Durham, England DH1 3LE;Department of Computer Science, University of Durham, Science Laboratories, Durham, England DH1 3LE;Dept. of Mathematics and Computer Science, Eindhoven University of Technology, Eindhoven, The Netherlands 5600 MB

  • Venue:
  • CSR '09 Proceedings of the Fourth International Computer Science Symposium in Russia on Computer Science - Theory and Applications
  • Year:
  • 2009

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Abstract

The 2-Disjoint Connected Subgraphs problem asks if a given graph has two vertex-disjoint connected subgraphs containing pre-specified sets of vertices. We show that this problem is NP-complete even if one of the sets has cardinality 2. The Longest Path Contractibility problem asks for the largest integer *** for which an input graph can be contracted to the path P *** on *** vertices. We show that the computational complexity of the Longest Path Contractibility problem restricted to P *** -free graphs jumps from being polynomially solvable to being NP-hard at ***= 6, while this jump occurs at ***= 5 for the 2-Disjoint Connected Subgraphs problem. We also present an exact algorithm that solves the 2-Disjoint Connected Subgraphs problem faster than ${\cal O}^*(2^n)$ for any n -vertex P *** -free graph. For ***= 6, its running time is ${\cal O}^*(1.5790^n)$. We modify this algorithm to solve the Longest Path Contractibility problem for P 6 -free graphs in ${\cal O}^*(1.5790^n)$ time.