学术文献库

A proper coloring of a graph is \emph{conflict-free} if, for every non-isolated vertex, some color is used exactly once on its neighborhood. Caro, Petruševski, and Škrekovski proved that every graph $G$ has a proper conflict-free coloring with at most $5Δ(G)/2$ colors and conjectured that $Δ(G)+1$ colors suffice for every connected graph $G$ with $Δ(G)\ge 3$. Our first main result is that even for list-coloring, $\left\lceil 1.6550826Δ(G)+\sqrt{Δ(G)}\right\rceil$ colors suffice for every graph $G$ with $Δ(G)\ge 10^{8}$; we also prove slightly weaker bounds for all graphs with $Δ(G)\ge 750$. These results follow from our more general framework on proper conflict-free list-coloring of a pair consisting of a graph $G$ and a "conflict" hypergraph ${\mathcal H}$. As another corollary of our results in this general framework, every graph has a proper $(\sqrt{30}+o(1))Δ(G)^{1.5}$-list-coloring such that every bi-chromatic component is a path on at most three vertices, where the number of colors is optimal up to a constant factor. Our proof uses a fairly new type of recursive counting argument called Rosenfeld counting, which is a variant of the Lovász Local Lemma or entropy compression. We also prove an asymptotically optimal result for a fractional analogue of our general framework for proper conflict-free coloring for pairs of a graph and a conflict hypergraph. A corollary states that every graph $G$ has a fractional $(1+o(1))Δ(G)$-coloring such that every fractionally bi-chromatic component has at most two vertices. In particular, it implies that the fractional analogue of the conjecture of Caro et al.\ holds asymptotically in a strong sense.