"""
undirected group -> connecteed + acyclic

directed rooted tree -> 面试中最常见的形式
                     -> 从root 可以到达任何点
                     -> 从root 到任意一点，只有一条path

binary tree: at most two children node

"""

"""
balanced binary tree: 
1. if a tree has n number of nodes, and it is balanced, then the height(level) of the tree = O(log(n))
"""

"""
complete binary tree: is a binary tree in which every level, except possibly the last, is completely filled,
                      and all nodes are as far left as possible

complete tree must be a bilanced tree

"""

"""

BST binary search tree

"""