English

Counting Odd Cycles in Graphs with Bounded Circumference

Combinatorics 2026-07-12 v1

Abstract

For an integer L2L\ge2, let a=L/2a=\lfloor L/2\rfloor. Let H(n,L)H(n,L) be the join of KaK_a and an independent set of order nan-a, with one extra edge in the independent set when LL is odd. We prove that, for every fixed s3s\ge3 and L2s+2L\ge2s+2, and for all sufficiently large nn, ex(n,C2s+1,CL+1)=N(C2s+1,H(n,L)). \operatorname{ex}(n,C_{2s+1},\mathcal{C}_{\ge L+1}) =N(C_{2s+1},H(n,L)). Together with the recent result of even-cycle by Zhao and Wang~[arXiv:2607.04357, 2026], this settles the conjecture of Zhu, Gy\H{o}ri, He, Lv, Salia and Xiao~[Bull. Lond. Math. Soc. 55 (2023)] on counting fixed cycles in graphs with bounded circumference. We also determine the corresponding maximum number of copies of odd cycles when a path is forbidden.

Cite

@article{arxiv.2607.10779,
  title  = {Counting Odd Cycles in Graphs with Bounded Circumference},
  author = {Xiamiao Zhao and Yuanpei Wang},
  journal= {arXiv preprint arXiv:2607.10779},
  year   = {2026}
}