Longest cycles in sparse random digraphs

Authors


  • Supported in part by USA-Israel BSF Grant (2006-322 and 2010-115); Israel Science Foundation (1063/08).

  • Supported in part by NSF grant (DMS-1101185); USA-Israel BSF Grant.

Abstract

Long paths and cycles in sparse random graphs and digraphs were studied intensively in the 1980's. It was finally shown by Frieze in 1986 that the random graph equation image with p = c/n has a cycle on at all but at most (1 + ε)cecn vertices with high probability, where ε = ε (c) → 0 as c → ∞. This estimate on the number of uncovered vertices is essentially tight due to vertices of degree 1. However, for the random digraph equation image no tight result was known and the best estimate was a factor of c/2 away from the corresponding lower bound. In this work we close this gap and show that the random digraph equation image with p = c/n has a cycle containing all but (2 + ε)ecn vertices w.h.p., where ε = ε (c) → 0 as c → ∞. This is essentially tight since w.h.p. such a random digraph contains (2eco(1))n vertices with zero in-degree or out-degree. © 2012 Wiley Periodicals, Inc. Random Struct. Alg., 2013

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