数据结构: 线索化二叉树

public class ThreadedBinaryTreeDemo {
    public static void main(String[] args) {
        // 先创建一棵二叉树
        ThreadedBinaryTree binaryTree = new ThreadedBinaryTree();

        // 创建需要的结点
        HeroNode root = new HeroNode(1, "宋江");
        HeroNode node2 = new HeroNode(3, "吴用");
        HeroNode node3 = new HeroNode(6, "卢俊义");
        HeroNode node4 = new HeroNode(8, "林冲");
        HeroNode node5 = new HeroNode(10, "关胜");
        HeroNode node6 = new HeroNode(14, "武松");

        binaryTree.setRoot(root);

        root.setLeft(node2);
        root.setRight(node3);

        // 设置父结点
        node2.setParent(root);
        node3.setParent(root);

        node2.setLeft(node4);
        node2.setRight(node5);

        // 设置父结点
        node4.setParent(node2);
        node5.setParent(node2);

        node3.setLeft(node6);

        // 设置父结点
        node6.setParent(node3);

        // 测试中序
        // 测试线索化
//        binaryTree.threadedNodes(root);  //8,3,10,1,14,6
//
//        HeroNode leftNode = node5.getLeft();
//        HeroNode rightNode = node5.getRight();
//        System.out.println(leftNode.getNo()+" "+leftNode.getName());
//        System.out.println(rightNode.getNo()+" "+rightNode.getName());
//
//        // 遍历线索化二叉树
//        binaryTree.threadedList();

        // 测试后序
        // 测试线索化
        binaryTree.threadedNodesPost(root);  //8,10,3,14,6,1

        HeroNode leftNode = node6.getLeft();
        HeroNode rightNode = node6.getRight();
        System.out.println(leftNode.getNo()+" "+leftNode.getName());
        System.out.println(rightNode.getNo()+" "+rightNode.getName());

        // 遍历线索化二叉树
        binaryTree.threadedListPost();
    }
}

class ThreadedBinaryTree{
    private HeroNode root;
    private HeroNode pre; // 线索化使用,总是指向当前结点的前驱结点

    public void setRoot(HeroNode root) {
        this.root = root;
    }

    // 对二叉树进行中序线索化
    public void threadedNodes(HeroNode node){
        if(null == node) {
            return;
        }

        // 中序线索化,先线索化左子树,再线索化当前结点,最后线索话右子树
        // 1.先线索化左子树
        threadedNodes(node.getLeft());

        // 2.再线索化当前结点
        if(node.getLeft() == null){
            node.setLeft(pre);
            node.setLeftType(1);
        }
        // 处理后继结点
        if(null != pre && pre.getRight() == null){
            // 让前驱结点的右指针指向当前结点
            pre.setRight(node);
            // 改变类型
            pre.setRightType(1);
        }

        // 让当前结点成为下一个结点的前驱结点
        pre = node;

        // 3.再线索化右子树
        threadedNodes(node.getRight());
    }

    // 中序遍历线索化二叉树的方法
    public void threadedList(){
        // 定义一个变量,存储当前遍历的结点,从root开始
        HeroNode node = root;
        while(null != node){

            while(node.getLeftType() == 0){
                node = node.getLeft();
            }

            System.out.println(node);

            while(node.getRightType() == 1){
                node = node.getRight();
                System.out.println(node);
            }

            node = node.getRight();
        }
    }

    // 对二叉树进行后序线索化
    public void threadedNodesPost(HeroNode node){
        if(null == node) {
            return;
        }

        // 后序线索化,先线索化左子树,再线索话右子树,最后线索化当前结点
        // 1.先线索化左子树
        threadedNodesPost(node.getLeft());

        // 2.再线索化右子树
        threadedNodesPost(node.getRight());

        // 3.最后线索化当前结点
        if(node.getLeft() == null){
            node.setLeft(pre);
            node.setLeftType(1);
        }
        // 处理后继结点
        if(null != pre && pre.getRight() == null){
            // 让前驱结点的右指针指向当前结点
            pre.setRight(node);
            // 改变类型
            pre.setRightType(1);
        }

        // 让当前结点成为下一个结点的前驱结点
        pre = node;
    }

    //后序遍历线索化二叉树可以参考该博客https://www.cnblogs.com/lishanlei/p/10707830.html 
    // 后序遍历线索化二叉树的方法, 后序遍历线索话二叉树需要利用父结点
    public void threadedListPost(){
        // 定义一个变量,存储当前遍历的结点,从root开始
        HeroNode node = root;
        while(null != node && node.getLeftType() == 0){
            node = node.getLeft();
        }

        while(null != node){
            //右节点是线索
            if(node.getRightType() == 1){
                System.out.println(node);
                pre = node;
                node = node.getParent();
            }else{
                //如果上个处理的节点是当前节点的右节点
                if(node.getRight() == pre){
                    System.out.println(node);
                    if(node == root){
                        return;
                    }

                    pre = node;
                    node = node.getParent();
                }else{
                    node = node.getRight();
                    while(null != node && node.getLeftType() == 0){
                        node = node.getLeft();
                    }

                }
            }
        }
    }
}

class HeroNode{
    private int no;
    private String name;
    private HeroNode left; // 默认为null
    private HeroNode right; // 默认为null

    //leftType  == 0, 表示指向左子树. leftType  == 1, 表示指向前驱结点.
    //rightType == 0, 表示指向右子树. rightType == 1, 表示指向后继结点.
    private int leftType;
    private int rightType;

    public HeroNode getParent() {
        return parent;
    }

    public void setParent(HeroNode parent) {
        this.parent = parent;
    }

    private HeroNode parent; // 父结点的指针

    public HeroNode(int no, String name) {
        this.no = no;
        this.name = name;
    }

    public int getLeftType() {
        return leftType;
    }

    public void setLeftType(int leftType) {
        this.leftType = leftType;
    }

    public int getRightType() {
        return rightType;
    }

    public void setRightType(int rightType) {
        this.rightType = rightType;
    }

    public int getNo() {
        return no;
    }

    public void setNo(int no) {
        this.no = no;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public HeroNode getLeft() {
        return left;
    }

    public void setLeft(HeroNode left) {
        this.left = left;
    }

    public HeroNode getRight() {
        return right;
    }

    public void setRight(HeroNode right) {
        this.right = right;
    }

    @Override
    public String toString() {
        return "HeroNode{" +
                "no=" + no +
                ", name='" + name + '\'' +
                '}';
    }
}