\(k\)-Frugal List Coloring of Planar Graphs Without Small Cycles

Qiming Fang1, Li Zhang1, Ming Chen1,2
1School of Mathematical Sciences, Tongji University, Shanghai 200092, China
2College of Mathematics Physics and Information Engineering, Jiaxing University, Zhejiang 314001, China

Abstract

A graph \( G \) is \( k \)-frugal colorable if there exists a proper vertex coloring of \( G \) such that every color appears at most \( k – 1 \) times in the neighborhood of \( v \). The \( k \)-frugal chromatic number, denoted by \( \chi_k(G) \), is the smallest integer \( l \) such that \( G \) is \( k \)-frugal colorable with \( l \) colors. A graph \( G \) is \( L \)-list colorable if there exists a coloring \( c \) of \( G \) for a given list assignment \( L = \{L(v) : v \in V(G)\} \) such that \( c(v) \in L(v) \) for all \( v \in V(G) \). If \( G \) is \( k \)-frugal \( L \)-colorable for any list assignment \( L \) with \( |L(v)| \geq l \) for all \( v \in V(G) \), then \( G \) is said to be \( k \)-frugal \( l \)-list-colorable. The smallest integer \( l \) such that the graph \( G \) is \( k \)-frugal \( l \)-list-colorable is called the \( k \)-frugal list chromatic number, denoted by \( \text{ch}_k(G) \). It is clear that \( \text{ch}_k(G) \geq \left\lceil \frac{\Delta(G)}{k – 1} \right\rceil + 1 \) for any graph \( G \) with maximum degree \( \Delta(G) \). In this paper, we prove that for any integer \( k \geq 4 \), if \( G \) is a planar graph with maximum degree \( \Delta(G) \geq 13k – 11 \) and girth \( g \geq 6 \), then \( \text{ch}_k(G) = \left\lceil \frac{\Delta(G)}{k – 1} \right\rceil + 1; \) and if \( G \) is a planar graph with girth \( g \geq 6 \), then \(\text{ch}_k(G) \leq \left\lceil \frac{\Delta(G)}{k – 1} \right\rceil + 2.\)

Keywords: \( k \)-frugal list coloring; Maximum degree; Planar graphs; Discharging.