Efficient approximation algorithms for shortest cycles in undirected graphs

  • Authors:
  • Andrzej Lingas;Eva-Marta Lundell

  • Affiliations:
  • Department of Computer Science, Lund University, 221 00 Lund, Sweden;Department of Computer Science, Lund University, 221 00 Lund, Sweden

  • Venue:
  • Information Processing Letters
  • Year:
  • 2009

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Abstract

We describe a simple combinatorial approximation algorithm for finding a shortest (simple) cycle in an undirected graph. Given an adjacency-list representation of an undirected graph G with n vertices and unknown girth k, our algorithm returns with high probability a cycle of length at most 2k for even k and 2k+2 for odd k, in time O(n^3^2logn). Thus, in general, it yields a 223 approximation. For a weighted, undirected graph, with non-negative edge weights in the range {1,2,...,M}, we present a simple combinatorial 2-approximation algorithm for a minimum weight (simple) cycle that runs in time O(n^2logn(logn+logM)).