A Path Variant of the Explorer Director Game on Graphs
Abigail Raz, Paddy Yang
TL;DR
This work introduces the path-length variant of the Explorer-Director game, defining $f_p(G,v)$ and comparing it with the classical $f_d(G,v)$. It proves that bipanpositionable graphs force $f_p(G,v)=4$, while hypercubes exhibit small $f_p$ values but potentially larger $f_d$ values, and constructs the CF$_n$ family where $f_p$ can greatly exceed $f_d$, and vice versa. The results provide upper and lower bounds, exact values for several regimes, and show that $f_p$ and $f_d$ can have arbitrarily large discrepancies, motivating further classification and exploration across graph families. The work advances understanding of path-based exploration games and opens questions about ratio growth, classification, and non-adaptive strategies in graph-theoretic pursuit games.
Abstract
The Explorer Director game, first introduced by Nedev and Muthukrishnan (2008), simulates a Mobile Agent exploring a ring network with an inconsistent global sense of direction. The two players, the Explorer and the Director, jointly control the movement of a token on the graph. During each turn, the Explorer calls any valid distance, $d$, with the aim of maximizing the number of vertices the token visits, and the Director moves the token to any vertex distance $d$ away with the aim of minimizing the number of visited vertices. The game, on graph $G$ with starting vertex $v$, ends when no new vertices could be visited assuming both players are playing optimally, and we denote the total number of visited vertices by $f_d(G,v)$. Since 2008, many authors have explored $f_d(G,v)$ for various graph families as well as analyses of complexity. In this work, we study a variation of this game focused on path lengths rather than distances. In this variant, if the token is on vertex $u$, the Explorer is now allowed to select any valid \emph{path length}, $l$, and the Director can now move the token to any vertex $v$ such that $G$ contains a $uv$ path of length $l$. The corresponding parameter is denoted by $f_p(G,v)$. In this paper, we explore how far apart $f_d(G,v)$ and $f_p(G,v)$ can be for various graph families, proving that for any $n$ there are graphs $G$ and $H$ with $f_p(G,v)-f_d(G,v)>n$ and $f_d(G,v)-f_p(G,v)>n$.