The computational complexity of the parallel knock-out problem

  • Authors:
  • Hajo Broersma;Matthew Johnson;Daniël Paulusma;Iain A. Stewart

  • Affiliations:
  • Department of Computer Science, Durham University, South Road, Durham, DH1 3LE, UK;Department of Computer Science, Durham University, South Road, Durham, DH1 3LE, UK;Department of Computer Science, Durham University, South Road, Durham, DH1 3LE, UK;Department of Computer Science, Durham University, South Road, Durham, DH1 3LE, UK

  • Venue:
  • Theoretical Computer Science
  • Year:
  • 2008

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Abstract

We consider computational complexity questions related to parallel knock-out schemes for graphs. In such schemes, in each round, each remaining vertex of a given graph eliminates exactly one of its neighbours. We show that the problem of whether, for a given bipartite graph, such a scheme can be found that eliminates every vertex is NP-complete. Moreover, we show that, for all fixed positive integers k=2, the problem of whether a given bipartite graph admits a scheme in which all vertices are eliminated in at most (exactly) k rounds is NP-complete. For graphs with bounded tree-width, however, both of these problems are shown to be solvable in polynomial time. We also show that r-regular graphs with r=1, factor-critical graphs and 1-tough graphs admit a scheme in which all vertices are eliminated in one round.