A constant factor approximation algorithm for generalized min-sum set cover

  • Authors:
  • Nikhil Bansal;Anupam Gupta;Ravishankar Krishnaswamy

  • Affiliations:
  • IBM T. J. Watson Research Center, Yorktown Heights, NY;Carnegie Mellon University, Pittsburgh, PA;IBM T. J. Watson Research Center

  • Venue:
  • SODA '10 Proceedings of the twenty-first annual ACM-SIAM symposium on Discrete Algorithms
  • Year:
  • 2010

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Abstract

Consider the following generalized min-sum set cover or multiple intents re-ranking problem proposed by Azar et al. (STOC 2009). We are given a universe of elements and a collection of subsets, with each set S having a covering requirement of K(S). The objective is to pick one element at a time such that the average covering time of the sets is minimized, where the covering time of a set S is the first time at which K(S) elements from it have been selected. There are two well-studied extreme cases of this problem: (i) when K(S) = 1 for all sets, we get the min-sum set cover problem, and (ii) when K(S) = |S| for all sets, we get the minimum-latency set cover problem. Constant factor approximations are known for both these problems. In their paper, Azar et al. considered the general problem and gave a logarithmic approximation algorithm for it. In this paper, we improve their result and give a simple randomized constant factor approximation algorithm for the generalized min-sum set cover problem.