离散数学课件 第七章 树trees
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第7章树trees
分类
§7.1 树
定义1:
T是集合A上一个二元关系,T称为树tree,
如果存在v0∈A,任意v∈A,v≠v0,到v0都有唯一一条路径,(v0, v0) T. T叫做根树,记做(T,v0)。
A中元素称为T的顶点vertex,T中元素称为边,v0称为根root。
定理1. 设(T,v0)是树,则
(a)T中没有回路。
(b)只有一个根v0。
(c)任意v∈A,v≠v0,v有入度1,v0入度是0。
证明:
定义2
层次level
v0的层次为0,v0的子女offspring层次为1,v0是子女的父母parent。
v i的层次为k,v i的子女offspring层次为k +1,v i是子女的父母parent,
T的最大层次称为高度height。
无子女的顶点叫叶leaf。
v i的子女叫同胞sibling,同胞如有长幼,从左到右,老大,老二,老三等,组成线性序,T称为有序树,ordered tree
定理2. 设(T,v0)是根树,则
(a)T反自反。
(b)T反对称。
(c)(a,b)∈T,(b,c)∈T ⇒ (a,c)∉T。
定义3:
n-树:每个顶点至多n个子女。
二叉树:2-树。
完全n-树:每个非叶顶点恰有n个子女。定义4
A rooted binary tree is a rooted tree in which every node has at most two children.
A full binary tree (sometimes proper binary tree or 2-tree) is a tree in which
every node other than the leaves has two children.
A perfect binary tree is a full binary tree in which all leaves are at the same depth or same level.[1] (This is ambiguously also called a complete binary tree.)
A 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.[2]
An infinite complete binary tree is a tree with levels, where for each level d the
number of existing nodes at level d is equal to 2d. The cardinal number of the set of all nodes is . The cardinal number of the set
of all paths is .
A balanced binary tree is a tree where the depth of all the sub-trees differs by at most 1.
定理3. 设(T,v0)是根树,v∈T,则T(v)是T的子树,T(v)的根是v。
Homework P248-249
18,19,20,21,26,28
§7.2标识树labeled trees
中缀表达式central operator expression(3-2×x)+((x-2))+(3+x))
定位树positional tree
定义
Positional n-tree is a n-tree whose vertex potentially has exactly n offspring ordered by1,2,…,n, but some of the offsprings may be missing.
定位3-树
每个顶点的子女都有一定位置。
定位2-树左右子树普通二叉树。
问题7.2.1
1)n个节点的定位二叉树有多少个?
2)如何枚举?
定位二叉树的计算机表示
Computer Representation of Binary Positional Trees
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Homework PP253-254
10,11,12,16,18,
§7.3 树的遍历tree searching(自学)二叉树的遍历
中序遍历的递归算法定义
(1)遍历左子树;
(2)访问根结点;
(3)遍历右子树。
先序遍历的递归算法定义
(1) 访问根结点;
(2) 遍历左子树;
(3) 遍历右子树。
后序遍历得递归算法定义
(1)遍历左子树;
(2)遍历右子树;
(3)访问根结点
树的搜索
深度优先搜索
广度优先搜索
启发式搜索
博弈树搜索
§7.4无向树undirected trees
无向图连通不含回路的图叫无向树例