Definition A tree is a collection of nodes. The collection can be empty: otherwise, a tree consists of (1) a distinguished node r, called the root; (2)and zero or more nonempty(sub)trees T1,., Tk, each of whose roots are connected by a directed edge from r Note:
chapter 9 GRAPH ALGORITHMs $I Definitions e G(V,E) where G: =graph, V=V(G): :=finite nonempty set of vertices, andE=E(G): : = finite set of edges. d' Undirected graph:(V;,vi)=(j,vi): =the same edge 6 Directed graph(digraph): :=2* I tailhead