Minimum Leaf Out-Branching Problems

  • Authors:
  • Gregory Gutin;Igor Razgon;Eun Jung Kim

  • Affiliations:
  • Department of Computer Science Royal Holloway, University of London, Egham, Surrey, UK TW20 0EX;Department of Computer Science, University College Cork, Ireland;Department of Computer Science Royal Holloway, University of London, Egham, Surrey, UK TW20 0EX

  • Venue:
  • AAIM '08 Proceedings of the 4th international conference on Algorithmic Aspects in Information and Management
  • Year:
  • 2008

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Abstract

Given a digraph D, the Minimum Leaf Out-Branching problem (MinLOB) is the problem of finding in Dan out-branching with the minimum possible number of leaves, i.e., vertices of out-degree 0. We prove that MinLOB is polynomial-time solvable for acyclic digraphs. In general, MinLOB is NP-hard and we consider three parameterizations of MinLOB. We prove that two of them are NP-complete for every value of the parameter, but the third one is fixed-parameter tractable (FPT). The FPT parametrization is as follows: given a digraph Dof order nand a positive integral parameter k, check whether Dcontains an out-branching with at most n驴 kleaves (and find such an out-branching if it exists). We find a problem kernel of order O(k·2k) and construct an algorithm of running time O(2O(klogk)+ n3), which is an `additive' FPT algorithm.