8.1 Trees

-->root,children, parent, siblings, leaf; level, degree of element 的基本概念

8.2 Binary Trees

-->什么样的tree是Binary Tree

8.3. Properties of Binary Tree

-->树的节点数与height的关系

-->full binary tree 到complete binary tree的概念

-->complete binary tree中parent 和child的序号的关系：也是用formula-based方法实现binary tree的基础

8.4. Representation of Binary Trees

-->Formula-based representation: array

:only efficient when the number of missing elements is small.

-->Linked Representation

::PreOrder, InOrder, PostOrder Traversal (recursive) use stack

::LevelOrder Traversal (not recursive) use queue

::它导致一个显著逻辑，假设一个算法的各个步骤能够之一样的的stack的方式来实现，然后可以使用recursive方
                 式来实现，该算法。