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Motivated by an old question of Gallai (1966) on the intersection of longest paths in a graph and the well-known conjectures of Lov\'{a}sz (1969) and Thomassen (1978) on the maximum length of paths and cycles in vertex-transitive graphs, we…

Combinatorics · Mathematics 2025-08-05 Sergey Norin , Raphael Steiner , Stephan Thomassé , Paul Wollan

We give an approximate Menger-type theorem for when a graph $G$ contains two $X-Y$ paths $P_1$ and $P_2$ such that $P_1 \cup P_2$ is an induced subgraph of $G$. More generally, we prove that there exists a function $f(d) \in O(d)$, such…

Combinatorics · Mathematics 2024-05-24 Sandra Albrechtsen , Tony Huynh , Raphael W. Jacobs , Paul Knappe , Paul Wollan

We investigate the problem $\#\mathsf{IndSub}(\Phi)$ of counting all induced subgraphs of size $k$ in a graph $G$ that satisfy a given property $\Phi$. This continues the work of Jerrum and Meeks who proved the problem to be…

Computational Complexity · Computer Science 2018-07-06 Marc Roth , Johannes Schmitt

A path partition (also referred to as a linear forest) of a graph $G$ is a set of vertex-disjoint paths which together contain all the vertices of $G$. An isolated vertex is considered to be a path in this case. The path partition…

Discrete Mathematics · Computer Science 2019-11-20 Uriel Feige , Ella Fuchs

The traditional complex network approach considers only the shortest paths from one node to another, not taking into account several other possible paths. This limitation is significant, for example, in urban mobility studies. In this short…

Discrete Mathematics · Computer Science 2022-10-10 Leonardo B. L. Santos , Luiz Max Carvalho , Giovanni G. Soares , Leonardo N. Ferreira , Igor M. Sokolov

B. Bollob\'{a}s and G. Brightwell and independently R. Shi proved the existence of a cycle through all vertices whose degrees at least $\frac{n}{2}$ in any $2$-connected graph of order $n$. Motivated by this result, we prove the existence…

Combinatorics · Mathematics 2025-02-12 Chengli Li , Leyou Xu

We show that for $d\ge d_0(\epsilon)$, with high probability, the random graph $G(n,d/n)$ contains an induced path of length $(3/2-\epsilon)\frac{n}{d}\log d$. This improves a result obtained independently by Luczak and Suen in the early…

Combinatorics · Mathematics 2021-02-19 Stefan Glock

A well-known question of Gallai (1966) asked whether there is a vertex which passes through all longest paths of a connected graph. Although this has been verified for some special classes of graphs such as outerplanar graphs, circular arc…

Combinatorics · Mathematics 2022-01-28 Bing Wei , Haidong Wu , Qinghong Zhao

Let $G$ be a connected graph. The eccentricity of a path $P$, denoted by ecc$_G(P)$, is the maximum distance from $P$ to any vertex in $G$. In the \textsc{Central path} (CP) problem our aim is to find a path of minimum eccentricity. This…

Combinatorics · Mathematics 2022-02-08 Renzo Gómez , Juan Gutiérrez

Reconfiguring two shortest paths in a graph means modifying one shortest path to the other by changing one vertex at a time so that all the intermediate paths are also shortest paths. This problem has several natural applications, namely:…

Data Structures and Algorithms · Computer Science 2021-12-15 Kshitij Gajjar , Agastya Vibhuti Jha , Manish Kumar , Abhiruk Lahiri

The connective constant mu of a graph is the exponential growth rate of the number of n-step self-avoiding walks starting at a given vertex. A self-avoiding walk is said to be forward (respectively, backward) extendable if it may be…

Combinatorics · Mathematics 2018-10-26 Geoffrey R. Grimmett , Alexander E. Holroyd , Yuval Peres

The goal of the paper is to give fine-grained hardness results for the Subgraph Isomorphism (SI) problem for fixed size induced patterns $H$, based on the $k$-Clique hypothesis that the current best algorithms for Clique are optimal. Our…

Computational Complexity · Computer Science 2022-09-07 Mina Dalirrooyfard , Virginia Vassilevska Williams

A connected subgraph of a graph is isometric if it preserves distances. In this short note, we provide counterexamples to several variants of the following general question: When a graph $G$ is edge covered by connected isometric subgraphs…

Combinatorics · Mathematics 2025-11-06 Paul Bastide , Julien Duron , Jędrzej Hodor , Weichan Liu , Xiangxiang Nie

We call a finite undirected graph minimally k-matchable if it has at least k distinct perfect matchings but deleting any edge results in a graph which has not. An odd subdivision of some graph G is any graph obtained by replacing every edge…

Combinatorics · Mathematics 2016-08-05 Gasper Fijavz , Matthias Kriesell

Motivated by the classical conjectures of Lov\'asz, Thomassen, and Smith, recent work has renewed interest in the study of longest cycles in important graph families, such as vertex-transitive and highly connected graphs. In particular,…

Combinatorics · Mathematics 2025-08-26 Jie Ma , Ziyuan Zhao

An antimagic labeling a connected graph $G$ is a bijection from the set of edges $E(G)$ to $\{1,2,\dots,|E(G)|\}$ such that all vertex sums are pairwise distinct, where the vertex sum at vertex $v$ is the sum of the labels assigned to edges…

Combinatorics · Mathematics 2024-05-09 Antoni Lozano , Mercè Mora , Carlos Seara , Joaquín Tey

A path graph is the intersection graph of paths in a tree. A directed path graph is the intersection graph of paths in a directed tree. Even if path graphs and directed path graphs are characterized very similarly, their recognition…

Data Structures and Algorithms · Computer Science 2025-05-07 Lorenzo Balzotti

The (strong) isometric path complexity is a recently introduced graph invariant that captures how arbitrary isometric paths (i.e., shortest paths) of a graph can be viewed as a union of a few ``rooted" isometric paths (i.e., isometric paths…

Combinatorics · Mathematics 2025-09-05 Dibyayan Chakraborty , Florent Foucaud

A $k$-path is a hypergraph P_k = e_1,e_2,...,e_k such that |e_i \cap e_j| = 1 if |j - i| = 1 and e_i \cap e_j is empty otherwise. A k-cycle is a hypergraph C_k = e_1,e_2,.. ,e_k obtained from a (k-1)-path e_1,e_2,...,e_{k-1} by adding an…

Combinatorics · Mathematics 2013-08-20 Alexandr Kostochka , Dhruv Mubayi , Jacques Verstraëte

For a simple graph $G$, let $n$ and $m$ denote the number of vertices and edges in $G$, respectively. The Erd\H{o}s-Gallai theorem for paths states that in a simple $P_k$-free graph, $m \leq \frac{n(k-1)}{2}$, where $P_k$ denotes a path…

Combinatorics · Mathematics 2025-05-08 Rajat Adak , L. Sunil Chandran