Graphs and Digraphs: A graph G = (V,E) is a structure that represents a discrete set V objects, called vertices or nodes, and a set of pairwise relations E between these objects, called edges. Edges may be directed from one vertex to another or may be undirected. The term “graph” means an undirected graph, and directed graphs are often called digraphs (see Fig. 1). Graphs and digraphs provide a...