Nonempty intersection of longest paths in 2K2-free graphs

Gili Golan, Songling Shan

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


In 1966, Gallai asked whether all longest paths in a connected graph share a common vertex. Counterexamples indicate that this is not true in general. However, Gallai's question is positive for certain well-known classes of connected graphs, such as split graphs, interval graphs, circular arc graphs, outerplanar graphs, and series- parallel graphs. A graph is 2K2-free if it does not contain two independent edges as an induced subgraph. In this short note, we show that, in nonempty 2K2-free graphs, every vertex of maximum degree is common to all longest paths. Our result implies that all longest paths in a nonempty 2K2-free graph have a nonempty intersection. In particular, it strengthens the result on split graphs, as split graphs are 2K2-free.

Original languageEnglish
Article number#P2.37
JournalElectronic Journal of Combinatorics
Issue number2
StatePublished - 8 Jun 2018
Externally publishedYes

ASJC Scopus subject areas

  • Theoretical Computer Science
  • Geometry and Topology
  • Discrete Mathematics and Combinatorics
  • Computational Theory and Mathematics
  • Applied Mathematics


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