English

Backward Arcs in Hamilton Oriented Cycles and Paths in Directed Graphs with Independence Number Two

Combinatorics 2026-03-25 v1 Discrete Mathematics

Abstract

In a digraph D=(V,A)D=(V,A), an oriented path is a sequence P=x1x2xpP=x_1x_2\dots x_p of distinct vertices such that either xixi+1Ax_ix_{i+1}\in A or xi+1xiAx_{i+1}x_{i}\in A or both for every i[p1]i\in [p-1]. If xixi+1Ax_ix_{i+1}\in A in PP, then xixi+1x_ix_{i+1} is a forward arc of PP; otherwise, xi+1xix_{i+1}x_{i} is a backward arc. The independence number α(D)\alpha(D) is the maximum integer pp such that DD has a set of pp vertices where there is no arc between any pair of vertices. A digraph is kk-connected if its underlying undirected graph is kk-connected. Freschi and Lo (JCT-B 2024) proved that every nn-vertex oriented graph with minimum degree δn/2\delta\ge n/2 has a Hamilton oriented cycle with at most nδn-\delta backward arcs. We prove that every 2-connected digraph DD with α(D)2\alpha(D)\le 2 has a Hamilton oriented cycle with at most five backward arcs, and every 1-connected digraph DD with α(D)2\alpha(D)\le 2 has a Hamilton oriented path with at most two backward arcs.

Keywords

Cite

@article{arxiv.2603.22993,
  title  = {Backward Arcs in Hamilton Oriented Cycles and Paths in Directed Graphs with Independence Number Two},
  author = {S. Gerke and Q. Guo and G. Gutin and Y. Hao and W. Veeranonchai and A. Yeo},
  journal= {arXiv preprint arXiv:2603.22993},
  year   = {2026}
}
R2 v1 2026-07-01T11:35:07.457Z