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Recontamination helps a lot to hunt a rabbit

The result's identifiers

  • Result code in IS VaVaI

    <a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F68407700%3A21240%2F23%3A00368685" target="_blank" >RIV/68407700:21240/23:00368685 - isvavai.cz</a>

  • Result on the web

    <a href="https://doi.org/10.4230/LIPICS.MFCS.2023.42" target="_blank" >https://doi.org/10.4230/LIPICS.MFCS.2023.42</a>

  • DOI - Digital Object Identifier

    <a href="http://dx.doi.org/10.4230/LIPICS.MFCS.2023.42" target="_blank" >10.4230/LIPICS.MFCS.2023.42</a>

Alternative languages

  • Result language

    angličtina

  • Original language name

    Recontamination helps a lot to hunt a rabbit

  • Original language description

    The textsc{Hunters and Rabbit} game is played on a graph $G$ where the Hunter player shoots at $k$ vertices in every round while the Rabbit player occupies an unknown vertex and, if it is not shot, must move to a neighbouring vertex after each round. The Rabbit player wins if it can ensure that its position is never shot. The Hunter player wins otherwise. The hunter number $h(G)$ of a graph $G$ is the minimum integer $k$ such that the Hunter player has a winning strategy (i.e., allowing him to win whatever be the strategy of the Rabbit player). This game has been studied in several graph classes, in particular in bipartite graphs (grids, trees, hypercubes...), but the computational complexity of computing $h(G)$ remains open in general graphs and even in more restricted graph classes such as trees. To progress further in this study, we propose a notion of monotonicity (a well-studied and useful property in classical pursuit-evasion games such as Graph Searching games) for the textsc{Hunters and Rabbit} game imposing that, roughly, a vertex that has already been shot ``must not host the rabbit anymore''. This allows us to obtain new results in various graph classes. More precisely, let the monotone hunter number $mh(G)$ of a graph $G$ be the minimum integer $k$ such that the Hunter player has a monotone winning strategy. We show that $pw(G) leq mh(G) leq pw(G)+1$ for any graph $G$ with pathwidth $pw(G)$, which implies that computing $mh(G)$, or even approximating $mh(G)$ up to an additive constant, is textsf{NP}-hard. Then, we show that $mh(G)$ can be computed in polynomial time in split graphs, interval graphs, cographs and trees. These results go through structural characterisations which allow us to relate the monotone hunter number with the pathwidth in some of these graph classes. In all cases, this allows us to specify the hunter number or to show that there may be an arbitrary gap between $h$ and $mh$, i.e., that monotonicity does not help. In particular, we show that, for every $kgeq 3$, there exists a tree $T$ with $h(T)=2$ and $mh(T)=k$. We conclude by proving that computing $h$ (resp., $mh$) is FPT~parameterised by the minimum size of a vertex cover.

  • Czech name

  • Czech description

Classification

  • Type

    D - Article in proceedings

  • CEP classification

  • OECD FORD branch

    10201 - Computer sciences, information science, bioinformathics (hardware development to be 2.2, social aspect to be 5.8)

Result continuities

  • Project

  • Continuities

    I - Institucionalni podpora na dlouhodoby koncepcni rozvoj vyzkumne organizace

Others

  • Publication year

    2023

  • Confidentiality

    S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů

Data specific for result type

  • Article name in the collection

    Proceedings of the 48th International Symposium on Mathematical Foundations of Computer Science

  • ISBN

    978-3-95977-292-1

  • ISSN

    1868-8969

  • e-ISSN

  • Number of pages

    14

  • Pages from-to

    591-604

  • Publisher name

    Schloss Dagstuhl--Leibniz-Zentrum fuer Informatik

  • Place of publication

    Dagstuhl

  • Event location

    Bordeaux

  • Event date

    Aug 28, 2023

  • Type of event by nationality

    WRD - Celosvětová akce

  • UT code for WoS article