线索二叉树（中序） Java实现

代码所示为下图二叉树

中序遍历：CBDAEF

C，D，F有两个空指针域，E有一个

步骤如下：

1.创建二叉树

2.创建头结点

3.中序遍历线索化

4.中序遍历此线索二叉树（非递归方式）

public class ThreadedBinaryTree {private static String [] array = {"A","B","C","","","D","","","E","","F","",""};private static int arrayIndex = 0;/** * 全局node，始终指向刚刚访问过的结点 */private static ThreadedBinaryNode preNode;/** * 1.参考创建二叉树,前序遍历输入 */public static ThreadedBinaryNode createThreadedBinaryTree(){String data = "";if(arrayIndex<array.length){data = array[arrayIndex];arrayIndex++;}ThreadedBinaryNode node = null;//data为空表示没有这个孩子if(data==null||data.equals("")){return node;}else{node = new ThreadedBinaryNode(data);node.setLchild(createThreadedBinaryTree());node.setRchild(createThreadedBinaryTree());node.setLtag(PointerTag.LINK);node.setRtag(PointerTag.LINK);return node;}}/** * 2.创建头结点，左孩子指向根节点 * @param rootNode */public static ThreadedBinaryNode createHeadNode(ThreadedBinaryNode rootNode){ThreadedBinaryNode headNode = new ThreadedBinaryNode();headNode.setLtag(PointerTag.LINK);headNode.setRtag(PointerTag.THREAD);//右孩子先指向自己，如果根节点不为null，指向中序遍历的最后一个结点，为null不用变headNode.setRchild(headNode);if(rootNode != null){//根结点不为null，头结点的左孩子指向根结点headNode.setLchild(rootNode);preNode = headNode;//开始中序遍历根结点inOrderTraverse(rootNode);//中序遍历的最后一个结点的后继指向头结点preNode.setRtag(PointerTag.THREAD);preNode.setRchild(headNode);//头结点的右孩子指向最后一个结点headNode.setRchild(preNode);}else{//根节点为null 左孩子指向自己headNode.setLchild(headNode);}return headNode;}/** * 3.中序遍历线索化 */public static void inOrderTraverse(ThreadedBinaryNode node){if(node != null){//递归左孩子线索化inOrderTraverse(node.getLchild());//结点处理if(null == node.getLchild()){//如果左孩子为空，设置tag为线索 THREAD，并把lchild指向刚刚访问的结点node.setLtag(PointerTag.THREAD);node.setLchild(preNode);}if(null == preNode.getRchild()){//如果preNode的右孩子为空，设置tag为线索THREADpreNode.setRtag(PointerTag.THREAD);preNode.setRchild(node);}//此处和前后两个递归的顺序不能改变，和结点处理同属一个级别preNode = node;//System.out.print(node.getData());//递归右孩子线索化inOrderTraverse(node.getRchild());}}/** * 4.中序遍历 非递归方式 * @param headNode */public static void inOrderTraverseNotRecursion(ThreadedBinaryNode headNode){ThreadedBinaryNode node = headNode.getLchild();while(headNode != node){//最左while(node.getLtag() == PointerTag.LINK){node = node.getLchild();}System.out.print(node.getData());//根while(node.getRtag() == PointerTag.THREAD && node.getRchild() !=headNode){node = node.getRchild();System.out.print(node.getData());}//右，不能打印是因为该子树下可能还存在最左node = node.getRchild();}}public static void main(String[] args) {//创建二叉树，约定前序输入ThreadedBinaryNode rootNode = createThreadedBinaryTree();//创建头结点，并中序遍历线索化ThreadedBinaryNode headNode = createHeadNode(rootNode);//中序遍历 非递归方式输出inOrderTraverseNotRecursion(headNode);}}class ThreadedBinaryNode{private String data;private ThreadedBinaryNode lchild;private ThreadedBinaryNode rchild;private PointerTag ltag;private PointerTag rtag;public String getData() {return data;}public void setData(String data) {this.data = data;}public ThreadedBinaryNode getLchild() {return lchild;}public void setLchild(ThreadedBinaryNode lchild) {this.lchild = lchild;}public ThreadedBinaryNode getRchild() {return rchild;}public void setRchild(ThreadedBinaryNode rchild) {this.rchild = rchild;}public PointerTag getLtag() {return ltag;}public void setLtag(PointerTag ltag) {this.ltag = ltag;}public PointerTag getRtag() {return rtag;}public void setRtag(PointerTag rtag) {this.rtag = rtag;}public ThreadedBinaryNode(String data) {super();this.data = data;}public ThreadedBinaryNode() {super();}@Overridepublic String toString() {return "ThreadedBinaryNode [data=" + data + ", ltag=" + ltag+ ", rtag=" + rtag + "]";}}/** * LINK :表示指向左右孩子的指针 * THREAD：表示指向前驱后继的线索 * @author cmdsm * */enum PointerTag{LINK , THREAD}