Bisecting a 4-connected graph with three resource sets

  • Authors:
  • Toshimasa Ishii;Kengo Iwata;Hiroshi Nagamochi

  • Affiliations:
  • Department of Information and Management Science, Otaru University of Commerce, Hokkaido 047-8501, Japan;Mazda Motor Corporation, Hiroshima 730-8670, Japan;Department of Applied Mathematics and Physics, Graduate School of Informatics, Kyoto University, Kyoto 606-8501, Japan

  • Venue:
  • Discrete Applied Mathematics
  • Year:
  • 2007

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Abstract

Let G=(V,E) be an undirected graph with a node set V and an arc set E. G has k pairwise disjoint subsets T"1,T"2,...,T"k of nodes, called resource sets, where |T"i| is even for each i. The partition problem with k resource sets asks to find a partition V"1 and V"2 of the node set V such that the graphs induced by V"1 and V"2 are both connected and |V"1@?T"i|=|V"2@?T"i|=|T"i|/2 holds for each i=1,2,...,k. The problem of testing whether such a bisection exists is known to be NP-hard even in the case of k=1. On the other hand, it is known that if G is (k+1)-connected for k=1,2, then a bisection exists for any given resource sets, and it has been conjectured that for k=3, a (k+1)-connected graph admits a bisection. In this paper, we show that for k=3, the conjecture does not hold, while if G is 4-connected and has K"4 as its subgraph, then a bisection exists and it can be found in O(|V|^3log|V|) time. Moreover, we show that for an arc-version of the problem, the (k+1)-edge-connectivity suffices for k=1,2,3.