A path in an edge-colored graph is rainbow if no two edges of it are colored the same. The graph is said to be rainbow connected if there is a rainbow path between every pair of vertices. If there is a rainbow shortest path between every pair of vertices, the graph is strong rainbow connected. We consider the complexity of the problem of deciding if a given edge-colored graph is rainbow or stro...

A path in an edge colored graph is said to be a rainbow path if no two edges on the path have the same color. An edge colored graph is (strongly) rainbow connected if there exists a (geodesic) rainbow path between every pair of vertices. The (strong) rainbow connectivity of a graph G, denoted by (src(G), respectively) rc(G) is the smallest number of colors required to edge color the graph such ...

A path in an edge colored graph is said to be a rainbow path if no two edges on the path have the same color. An edge colored graph is (strongly) rainbow connected if there exists a (geodesic) rainbow path between every pair of vertices. The (strong) rainbow connectivity of a graph G, denoted by (src(G), respectively) rc(G) is the smallest number of colors required to edge color the graph such ...

In this paper we define a construct called a time-graph. A complete time-graph of order n is the cartesian product of a complete graph with n vertices and a linear graph with n vertices. A time-graph of order n is given by a subset of the set of edges E(n) of such a graph. The notion of a hamiltonian time-graph is defined in a natural way and we define the Hamiltonian time-graph problem (HAMTG)...

We consider the minimum-weight path between any pair of nodes of the n-vertex complete graph in which the weights of the edges are i.i.d. exponentially distributed random variables. We show that the longest of these minimum-weight paths has about α logn edges where α ≈ 3.5911 is the unique solution of the equation α logα − α = 1. This answers a question left open by Janson [8].

A path separator of a graph G is a set of paths P = {P1, . . . , Pt} such that for every pair of edges e, f ∈ E(G), there exist paths Pe, Pf ∈ P such that e ∈ E(Pe), f 6∈ E(Pe), e 6∈ E(Pf ) and f ∈ E(Pf ). The path separation number of G, denoted psn(G), is the smallest number of paths in a path separator. We shall estimate the path separation number of several graph families, including complet...

An edge-colored graph G is rainbow connected if any two vertices are connected by a path whose edges have distinct colors. The rainbow connection number of a connected graph G, denoted by rc(G), is the smallest number of colors that are needed in order to make G rainbow connected. It was proved that computing rc(G) is an NP-Hard problem, as well as that even deciding whether a graph has rc(G) =...

Proof. Clearly, this problem is in NP, since one can easily guess the coverage path of the robot and then verify its probability of surviving it in polynomial time. To prove its NP-hardness, we use a reduction from the Hamiltonian path problem on grid graphs. A grid graph is a finite node-induced subgraph of the infinite two-dimensional integer grid (see Figure 1 for an example of a general gri...

A grid graph is a node-induced finite subgraph of the infinite grid. It is rectangular if its set of nodes is the product of two intervals. Given a rectangular grid graph and two of its nodes, we give necessary and sufficient conditions for the graph to have a Hamilton path between these two nodes. In contrast, the Hamilton path (and circuit) problem for general grid graphs is shown to be NP-co...