Greedy in approximation algorithms

  • Authors:
  • Julián Mestre

  • Affiliations:
  • Department of Computer Science, University of Maryland, College Park, MD

  • Venue:
  • ESA'06 Proceedings of the 14th conference on Annual European Symposium - Volume 14
  • Year:
  • 2006

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Abstract

The objective of this paper is to characterize classes of problems for which a greedy algorithm finds solutions provably close to optimum. To that end, we introduce the notion of k-extendible systems, a natural generalization of matroids, and show that a greedy algorithm is a 1/k-factor approximation for these systems. Many seemly unrelated problems fit in our framework, e.g.: b-matching, maximum profit scheduling and maximum asymmetric TSP. In the second half of the paper we focus on the maximum weight b- atching problem. The problem forms a 2-extendible system, so greedy gives us a 1/2 -factor solution which runs in O(m logn) time. We improve this by providing two linear time approximation algorithms for the problem: a 1/2 -factor algorithm that runs in O(b m) time, and a (2/3- ε) -factor algorithm which runs in expected O(bm log 1/ε) time.