GraphsNew

代码说明：

  A graph G = (V, E) consists of a set of vertices, V, and a set of edges, E, where each edge is a pair (v,w) s.t. v,w  V Vertices are sometimes called nodes, edges are sometimes called arcs. If the edge pair is ordered then the graph is called a directed graph (also called digraphs) . We also call a normal graph (which is not a directed graph) an undirected graph. When we say graph we mean that it is an undirected graph.