树是一种递归结构！
具有n个节点的数据集。
常见由二叉树，二叉查找树，红黑树，B+tree，B-tree等。
下面通过一段代码来实现简单的二叉树：
首先二叉树：
每个节点至多由两个子树。i层的节点总数不大于2^i-1。度为2就指的是子树为2.
层数和深度是指树的下延数。
二叉树又分为完全二叉树（除了最后一层其它各层的子树都满）和满二叉树（与完全二叉树不同在于所有层数都是满的达到了此树的度）。
//定义二叉树对象
public class BinaryTree {
private TreeNode root;// 根节点
public BinaryTree() {
// TODO Auto-generated constructor stub
}
public BinaryTree(TreeNode root) {
this.root = root;
}
public TreeNode getRoot() {
return root;
}
public void setRoot(TreeNode root) {
this.root = root;
}
/*
* 定义节点内部类
*/
private static class TreeNode {
// 数据部分
private String data = null;
// 左节点的引用
private TreeNode left;
// 右节点的引用
private TreeNode right;
public TreeNode() {
// TODO Auto-generated constructor stub
}
//含参构造
public TreeNode(String data, TreeNode left, TreeNode right) {
super();
this.data = data;
this.left = left;
this.right = right;
}
public String getData() {
return data;
}
public void setData(String data) {
this.data = data;
}
public TreeNode getLeft() {
return left;
}
public void setLeft(TreeNode left) {
this.left = left;
}
public TreeNode getRight() {
return right;
}
public void setRight(TreeNode right) {
this.right = right;
}
}
/**
* 返回父节点
*
* @param element
* @return
*/
public TreeNode GetParent(TreeNode element) {
return (root==null||root==element)
?null:parent(root,element);
}
public TreeNode parent(TreeNode subTree, TreeNode element) {
if (subTree==null) return null;
if (subTree.getLeft()==element||subTree.getRight()==element)
//返回父节点地址
return subTree;
TreeNode p;
//现在左子树中找，如果左子树中没有找到，才到右子树去找
if ((p=parent(subTree.getLeft(), element))!=null)
//递归在左子树中搜索
return p;
else
//递归在右子树中搜索
return parent(subTree.getRight(), element);
}
/**
* 节点个数
* @return*/
public int getSize(){
return getNum(root);
}
private int getNum(TreeNode node) {
if (node==null)
{
return 0;
}
else
{
int i=getNum(node.getLeft());
int j=getNum(node.getRight());
return j+i+1;
}
}
/**
* 获取树的高度
* @return*/
public int getHeight()
{
return getHeight(root);
}
private int getHeight(TreeNode node)
{
if (node==null)
return 0;
else
{
int i=getHeight(node.getLeft());
int j=getHeight(node.getRight());
return (i<j)?(j+1):(i+1);
}
}
/**
* 前序遍历
*
* @param node*/
public void preOrder(TreeNode node)
{
if (node!=null) {
System.out.println(node.getData());
preOrder(node.getLeft());
preOrder(node.getRight());
}
}
/**
* 中序遍历
*
* @param node*/
public void inOrder(TreeNode node)
{
if (node!=null) {
inOrder(node.getLeft());
System.out.println(node.getData());
inOrder(node.getRight());
}
}
/**
* 后序遍历
*
* @param node*/
public void postOrder(TreeNode node)
{
if (node!=null) {
postOrder(node.getLeft());
postOrder(node.getRight());
System.out.println(node.getData());
}
}
/**
* 插入操作
* @param String value*/
public void insert(String value){
TreeNode newNode = new TreeNode(value,null,null);
if (root==null) {
root=newNode;
root.setLeft(null);
root.setRight(null);
}else{
TreeNode currentNode=root;
TreeNode parentNode;
while (true) {
parentNode=currentNode;
//放右子树节点
if (currentNode==null) {
currentNode.data=value;
currentNode.left=null;
currentNode.right=null;
return;
}
if (currentNode.getLeft()==null) {
currentNode=currentNode.left;
}else if (currentNode.getRight()==null) {
currentNode=currentNode.right;
}else {
if (getHeight(root.right)>getHeight(root.left)) {
}
}
}
}
}
public static void main(String[] args) {
TreeNode l12 = new TreeNode("left12", null, null);
TreeNode r12 = new TreeNode("right12", null, null);
TreeNode l22 = new TreeNode("left22", null, null);
TreeNode r22 = new TreeNode("right22", null, null);
TreeNode l1 = new TreeNode("left1",l12,r12);//根节点左子树
TreeNode r1 = new TreeNode("right1",l22,r22);//根节点右子树
//创建根节点
TreeNode root = new TreeNode("root",l1,r1);
BinaryTree bt = new BinaryTree(root);
System.out.println("======先序遍历======");
bt.preOrder(bt.getRoot());
System.out.println("======中序遍历======");
bt.inOrder(bt.getRoot());
System.out.println("======后序遍历======");
bt.postOrder(bt.getRoot());
System.out.println("===========");
System.out.println(bt.getHeight());
System.out.println(bt.getSize());
System.out.println(bt.GetParent(r22).getData());
}
}
//理解的还是不够深入，对于一些具体细节还是由疑问？？？