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A parity path in a vertex colouring of a graph is a path along which each colour is used an even number of times. Let χ p (G) be the least number of colours in a proper vertex colouring of G having no parity path. It is proved that for any graph G we have the following tight bounds χ(G) ≤ χ p (G) ≤ |V (G)| − α(G) + 1, where χ(G) and α(G) are the chromatic(More)
The well-known lower bound on the independence number of a graph due 1981) can be established as a performance guarantee of two natural and simple greedy algorithms or of a simple randomized algorithm. We study possible generalizations and improvements of these approaches using vertex weights and discuss conditions on so-called potential functions p G : V(More)
A complete k-coloring of a graph G = (V, E) is an assignment ϕ : V → {1,. .. , k} of colors to the vertices such that no two vertices of the same color are adjacent, and the union of any two color classes contains at least one edge. Three extensively investigated graph invariants related to complete colorings are the minimum and maximum number of colors in(More)
In graph cleaning problems, brushes clean a graph by traversing it subject to certain rules. We consider the process where at each time step, a vertex that has at least as many brushes as incident, contaminated edges, sends brushes down these edges to clean them. Various problems arise, such as determining the minimum number of brushes (called the brush(More)
In this work we consider the edge searching problem for vertex-weighted graphs with arbitrarily fast and invisible fugitive. The weight function $${\omega }$$ ω provides for each vertex $$v$$ v the minimum number of searchers required to guard $$v$$ v , i.e., the fugitive may not pass through $$v$$ v without being detected only if at least $${\omega }(v)$$(More)
A vertex ranking of a graph G is an assignment of positive integers (colors) to the vertices of G such that each path connecting two vertices of the same color contains a vertex of a higher color. Our main goal is to find a vertex ranking using as few colors as possible. Considering on-line algorithms for vertex ranking of split graphs, we prove that the(More)