In the (k, lambda)-subgraph problem, we are given an undirected graph G = (V, E) with edge costs and two positive integers k and., and the goal is to find a minimum cost simple.-edge-connected subgraph of G with at le...
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In the (k, lambda)-subgraph problem, we are given an undirected graph G = (V, E) with edge costs and two positive integers k and., and the goal is to find a minimum cost simple.-edge-connected subgraph of G with at least k nodes. This generalizes several classical problems, such as the minimum cost k-spanning tree problem, or k-MST (which is a (k, 1)-subgraph), and the minimum cost lambda-edge-connected spanning subgraph (which is a (vertical bar V(G)vertical bar, lambda)-subgraph). The only previously known results on this problem [L. C. Lau, J. S. Naor, M. R. Salavatipour, and M. Singh, SIAM J. Comput., 39 (2009), pp. 1062-1087], [C. Chekuri and N. Korula, in Proceedings of the IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS), Bangalore, India, LIPIcs 2, Schloss Dagstuhl-Leibniz-Zentrum fur Informatik, Dagstuhl, Germany, 2008, pp. 119-130] show that the (k, 2)-subgraph problem has an O(log(2) n)-approximation (even for 2-node-connectivity) and that the (k, lambda)-subgraph problem in general is almost as hard as the densest k-subgraph problem. In this paper we show that if the edge costs are metric (i.e., satisfy the triangle inequality), like in the k-MST problem, then there is an O(1)-approximation algorithm for the (k, lambda)-subgraph problem. This essentially generalizes the k-MST constant factor approximability to higher connectivity.
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