5.5.3 Rooted tree and binary tree 4 Definition 25: A directed graph is a directed tree if the graph is a tree in the underlying undirected graph. .s Definition 26: A rooted tree is a directed tree if there are exactly a vertex that is 0 in-degree, and other vertices that are I in-degree. The vertex of 0 in-degree is called root. And the vertices of 0 out-degree are called leaves. The vertices that are not 0 out-degree are called internal vertices &o There is a unique path from the root to each vertex of the rooted tree by the definition 265.5.3 Rooted tree and binary tree ❖ Definition 25: A directed graph is a directed tree if the graph is a tree in the underlying undirected graph. ❖ Definition 26: A rooted tree is a directed tree if there are exactly a vertex that is 0 in-degree, and other vertices that are 1 in-degree. The vertex of 0 in-degree is called root. And the vertices of 0 out-degree are called leaves. The vertices that are not 0 out-degree are called internal vertices. ❖ There is a unique path from the root to each vertex of the rooted tree by the definition 26