树的结构

- Binary Trees:AA Tree, AVL Tree, Binary Search Tree, Binary Tree, Cartesian Tree,left child/right sibling tree, order statistic tree, Pagoda
 *       ,
 *      , ...
 *
 *     B Trees:
 *       B Tree, B+ Tree, B* Tree, B Sharp Tree, Dancing Tree, 2-3 Tree, ...
 *
 *     Heaps:
 *       Heap, Binary Heap, Weak Heap, Binomial Heap, Fibonacci Heap, Leonardo
 *       Heap, 2-3 Heap, Soft Heap, Pairing Heap, Leftist Heap, Treap, ...
 *
 *     Trees:
 *       Trie, Radix Tree, Suffix Tree, Suffix Array, FM-index, B-trie, ...
 *
 *     Multi-way Trees:
 *       Ternary Tree, K-ary tree, And-or tree, (a,b)-tree, Link/Cut Tree, ...
 *
 *     Space Partitioning Trees:
 *       Segment Tree, Interval Tree, Range Tree, Bin, Kd Tree, Quadtree,
 *       Octree, Z-Order, UB-Tree, R-Tree, X-Tree, Metric Tree, Cover Tree, ...
 *
 *     Application-Specific Trees:
 *       Abstract Syntax Tree, Parse Tree, Decision Tree, Minimax Tree, ...
/**
 * The remaining two data structures we are going to cover are both in the
 * "tree" family.
 *
 * Much like real life, there are many different types of tree data structures.
 *

 *
 * Little did you know you'd be studying dendrology today... and thats not even
 * all of them. But don't let any of this scare you, most of those don't matter
 * at all. There were just a lot of Computer Science PhDs who had something to
 * prove.
 *
 * Trees are much like graphs or linked lists except they are "unidirectional".
 * All this means is that they can't have loops of references.
 *
 *        Tree:                Not a Tree:
 *
 *          A                        A
 *        ↙   ↘                    ↗   ↘
 *      B       C                B ←–––– C
 *
 * If you can draw a loop between connected nodes in a tree... well, you don't
 * have a tree.
 *
 * Trees have many different uses, they can used to optimize searching or
 * sorting. They can organize programs better. They can give you a
 * representation that is easier to work with.
 */

一个节点数>5 的树，至少删去 1 个结点才可以使该树不连通。