An Improved Approximation Algorithm for Spanning Star Forest in Dense Graphs

  • Jing He
  • Hongyu Liang
Part of the Lecture Notes in Computer Science book series (LNCS, volume 6509)


A spanning subgraph of a given graph G is called a spanning star forest of G if it is a collection of node-disjoint trees of depth at most 1 (such trees are called stars). The size of a spanning star forest is the number of leaves in all its components. The goal of the spanning star forest problem [12] is to find the maximum-size spanning star forest of a given graph.

In this paper, we study this problem in c-dense graphs, where for c ∈ (0,1), a graph of n vertices is called c-dense if it contains at least cn2/2 edges [2]. We design a \((\alpha+(1-\alpha)\sqrt{c}-\epsilon)\)-approximation algorithm for spanning star forest in c-dense graphs for any ε> 0, where \(\alpha=\frac{193}{240}\) is the best known approximation ratio of the spanning star forest problem in general graphs [3]. Thus, our approximation ratio outperforms the best known bound for this problem when dealing with c-dense graphs. We also prove that for any c ∈ (0,1), there is a constant ε = ε(c) > 0 such that approximating spanning star forest in c-dense graphs within a factor of 1 − ε is NP-hard. We then demonstrate that for weighted versions (both node- and edge- weighted) of this problem, we cannot get any approximation algorithm with strictly better performance guarantee in c-dense graphs than that of the best possible approximation algorithm for general graphs. Finally, we give strong hardness-of-approximation results for a closely related problem, the minimum dominating set problem, in c-dense graphs.


spanning star forest approximation algorithm dense graphs 


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Copyright information

© Springer-Verlag Berlin Heidelberg 2010

Authors and Affiliations

  • Jing He
    • 1
  • Hongyu Liang
    • 1
  1. 1.Institute for Theoretical Computer ScienceTsinghua UniversityBeijingChina

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