Covering with Clubs: Complexity and Approximability

  • Riccardo Dondi
  • Giancarlo Mauri
  • Florian SikoraEmail author
  • Italo Zoppis
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 10979)


Finding cohesive subgraphs in a network is a well-known problem in graph theory. Several alternative formulations of cohesive subgraph have been proposed, a notable example being s-club, which is a subgraph where each vertex is at distance at most s to the others. Here we consider the problem of covering a given graph with the minimum number of s-clubs. We study the computational and approximation complexity of this problem, when s is equal to 2 or 3. First, we show that deciding if there exists a cover of a graph with three 2-clubs is NP-complete, and that deciding if there exists a cover of a graph with two 3-clubs is NP-complete. Then, we consider the approximation complexity of covering a graph with the minimum number of 2-clubs and 3-clubs. We show that, given a graph \(G=(V,E)\) to be covered, covering G with the minimum number of 2-clubs is not approximable within factor \(O(|V|^{1/2 -\varepsilon })\), for any \(\varepsilon >0\), and covering G with the minimum number of 3-clubs is not approximable within factor \(O(|V|^{1 -\varepsilon })\), for any \(\varepsilon >0\). On the positive side, we give an approximation algorithm of factor \(2|V|^{1/2}\log ^{3/2} |V|\) for covering a graph with the minimum number of 2-clubs.


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Copyright information

© Springer International Publishing AG, part of Springer Nature 2018

Authors and Affiliations

  • Riccardo Dondi
    • 1
  • Giancarlo Mauri
    • 2
  • Florian Sikora
    • 3
    Email author
  • Italo Zoppis
    • 2
  1. 1.Università degli Studi di BergamoBergamoItaly
  2. 2.Università degli Studi di Milano-BicoccaMilanItaly
  3. 3.Université Paris-Dauphine, PSL Research University, CNRS UMR 7243, LAMSADEParisFrance

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