The paper gives an account of previous and recent attempts to determine the order of a smallest graph not containing K5 and such that every 2-coloring of its edges results in a monochromatic triangle. A new 14-vertex K4-free graph with the same Ramsey property in the vertex coloring case is found. This yields a new construction of one of the only two known 15-vertex (3,3)-Ramsey graphs not cont...

We present a branching scheme for some Vertex Coloring Problems based on a new graph operator called extension. The extension operator is used to generalize the branching scheme proposed by Zykov for the basic problem to a broad class of coloring problems, such as the graph multicoloring, where each vertex requires a multiplicity of colors, the graph bandwidth coloring, where the colors assigne...

For a graph G and a vertex-coloring c : V (G) → {1, 2, . . . , k}, the color code of a vertex v is the (k + 1)-tuple (a0, a1, . . . , ak), where a0 = c(v), and for 1 ≤ i ≤ k, ai is the number of neighbors of v colored i. A recognizable coloring is a coloring such that distinct vertices have distinct color codes. The recognition number of a graph is the minimum k for which G has a recognizable k...

The q-Coloring problem asks whether the vertices of a graph can be properly colored with q colors. Lokshtanov et al. [SODA 2011] showed that q-Coloring on graphs with a feedback vertex set of size k cannot be solved in time O∗((q− ε)), for any ε > 0, unless the Strong Exponential-Time Hypothesis (SETH) fails. In this paper we perform a fine-grained analysis of the complexity of q-Coloring with ...

We design fast dynamic algorithms for proper vertex and edge colorings in a graph undergoing edge insertions and deletions. In the static setting, there are simple linear time algorithms for (∆ + 1)vertex coloring and (2∆ − 1)-edge coloring in a graph with maximum degree ∆. It is natural to ask if we can efficiently maintain such colorings in the dynamic setting as well. We get the following th...

On-line graph coloring algorithms have been defined in [2] as algorithms whose input graph is presented vertex by vertex, at each step the current vertex is given with all adjacencies to previously given vertices. The algorithm must color irrevocably the current vertex and has to maintain a proper vertex coloring. The simplest and best understood example of an on-line coloring algorithm is the ...

For a mixed hypergraphH= (X,C,D), where C andD are set systems over the vertex set X, a coloring is a partition of X into ‘color classes’such that everyC ∈ Cmeets some class in more than one vertex, and everyD ∈ D has a nonempty intersection with at least two classes.A vertex-order x1, x2, . . . , xn onX (n=|X|) is uniquely colorable if the subhypergraph induced by {xj : 1 j i} has precisely on...

A dynamic k-coloring of a graphG is a proper k-coloring of the vertices ofG such that every vertex of degree at least 2 in G will be adjacent to vertices with at least two different colors. The smallest number k for which a graph G has a dynamic k-coloring is the dynamic chromatic number χd(G). In this paper, we investigate the behavior of χd(G), the bounds for χd(G), the comparison between χd(...

Let c be a vertex k -coloring on a connected graph G(V,E) . Let Π = {C1, C2, ..., Ck} be the partition of V (G) induced by the coloring c . The color code cΠ(v) of a vertex v in G is (d(v, C1), d(v, C2), ..., d(v, Ck)), where d(v, Ci) = min{d(v, x)|x ∈ Ci} for 1 ≤ i ≤ k. If any two distinct vertices u, v in G satisfy that cΠ(u) 6= cΠ(v), then c is called a locating k-coloring of G . The locatin...