数据结构--线索化二叉树（Java）

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说明

• n个结点的二叉链表中含有n+1 【公式 2n-(n-1)=n+1】 个空指针域。利用二叉链表中的空指针域，存放指向该结点在某种遍历次序下的前驱和后继结点的指针（这种附加的指针称为"线索"）
• 这种加上了线索的二叉链表称为线索链表，相应的二叉树称为线索二叉树(Threaded BinaryTree)。根据线索性质的不同，线索二叉树可分为前序线索二叉树、中序线索二叉树和后序线索二叉树三种
• 一个结点的前一个结点，称为前驱结点
• 一个结点的后一个结点，称为后继结点

代码

package cn.guizimo.thread.tree;

/**
 * @author guizimo
 * @date 2020/8/7 11:08 上午
 */
public class ThreadTree {
    public static void main(String[] args) {
        //设置节点
        HeroNode root = new HeroNode(1, "tom");
        HeroNode node2 = new HeroNode(3, "jack");
        HeroNode node3 = new HeroNode(6, "smith");
        HeroNode node4 = new HeroNode(8, "mary");
        HeroNode node5 = new HeroNode(10, "king");
        HeroNode node6 = new HeroNode(14, "dim");

        //设置二叉树
        root.setLeft(node2);
        root.setRight(node3);
        node2.setLeft(node4);
        node2.setRight(node5);
        node3.setLeft(node6);

        //线索化
        ThreadedBinaryTree threadedBinaryTree = new ThreadedBinaryTree();
        threadedBinaryTree.setRoot(root);
        threadedBinaryTree.threadedNodes();

        //遍历
        threadedBinaryTree.threadedList();
    }
}


/**
 * 二叉树
 */
class ThreadedBinaryTree {
    //根节点
    private HeroNode root;

    //辅助节点
    private HeroNode pre = null;

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

    public void threadedNodes() {
        this.threadedNodes(root);
    }

    //中序遍历
    public void threadedList() {
        HeroNode node = root;
        while (node != null) {
            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();
        }
    }

    //线索化
    public void threadedNodes(HeroNode node) {
        if(node == null) {
            return;
        }
        threadedNodes(node.getLeft());
        if(node.getLeft() == null) {
            node.setLeft(pre);
            node.setLeftType(1);
        }
        if (pre != null && pre.getRight() == null) {
            pre.setRight(node);
            pre.setRightType(1);
        }
        pre = node;
        threadedNodes(node.getRight());
    }

    //删除二叉树的节点
    public void delNode(int no) {
        if (root != null) {
            if (root.getNo() == no) {
                root = null;
            } else {
                root.delNode(no);
            }
        } else {
            System.out.println("二叉树为空");
        }
    }

    //前序
    public void preOrder() {
        if (this.root != null) {
            this.root.preOrder();
        } else {
            System.out.println("二叉树为空");
        }
    }

    //中序
    public void infixOrder() {
        if (this.root != null) {
            this.root.infixOrder();
        } else {
            System.out.println("二叉树为空");
        }
    }

    //后序
    public void postOrder() {
        if (this.root != null) {
            this.root.postOrder();
        } else {
            System.out.println("二叉树为空");
        }
    }

    //前序查找
    public HeroNode preOrderSearch(int no) {
        if (root != null) {
            return root.preOrderSearch(no);
        } else {
            return null;
        }
    }

    //中序查找
    public HeroNode infixOrderSearch(int no) {
        if (root != null) {
            return root.infixOrderSearch(no);
        } else {
            return null;
        }
    }

    //后序查找
    public HeroNode postOrderSearch(int no) {
        if (root != null) {
            return this.root.postOrderSearch(no);
        } else {
            return null;
        }
    }
}


/**
 * 节点
 */
class HeroNode {
    private int no;
    private String name;
    private HeroNode left;
    private HeroNode right;

    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;
    }

    private int leftType;
    private int rightType;

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

    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 + '\'' +
                '}';
    }

    //删除节点
    public void delNode(int no) {
        //判读左节点是否为空，找到
        if (this.left != null && this.left.no == no) {
            this.left = null;
            return;
        }
        //判断右节点，找到
        if (this.right != null && this.right.no == no) {
            this.right = null;
            return;
        }
        //判断左节点，未找到，递归
        if (this.left != null) {
            this.left.delNode(no);
        }
        //判断右节点，未找到，递归
        if (this.right != null) {
            this.right.delNode(no);
        }
    }

    //前序
    public void preOrder() {
        System.out.println(this);
        if (this.left != null) {
            this.left.preOrder();
        }
        if (this.right != null) {
            this.right.preOrder();
        }
    }

    //中序
    public void infixOrder() {
        if (this.left != null) {
            this.left.infixOrder();
        }
        System.out.println(this);
        if (this.right != null) {
            this.right.infixOrder();
        }
    }

    //后序
    public void postOrder() {
        if (this.left != null) {
            this.left.postOrder();
        }
        if (this.right != null) {
            this.right.postOrder();
        }
        System.out.println(this);
    }

    //前序遍历查找
    public HeroNode preOrderSearch(int no) {
        if (this.no == no) {
            return this;
        }
        HeroNode resNode = null;
        //判断左子树
        if (this.left != null) {
            resNode = this.left.preOrderSearch(no);
        }
        if (resNode != null) {
            return resNode;
        }
        //判断右子树
        if (this.right != null) {
            resNode = this.right.preOrderSearch(no);
        }
        return resNode;
    }

    //中序遍历查找
    public HeroNode infixOrderSearch(int no) {
        HeroNode resNode = null;
        if (this.left != null) {
            resNode = this.left.infixOrderSearch(no);
        }
        if (resNode != null) {
            return resNode;
        }
        if (this.no == no) {
            return this;
        }
        if (this.right != null) {
            resNode = this.right.infixOrderSearch(no);
        }
        return resNode;
    }

    //后序遍历查找
    public HeroNode postOrderSearch(int no) {
        HeroNode resNode = null;
        if (this.left != null) {
            resNode = this.left.postOrderSearch(no);
        }
        if (resNode != null) {
            return resNode;
        }
        if (this.right != null) {
            resNode = this.right.postOrderSearch(no);
        }
        if (resNode != null) {
            return resNode;
        }
        if (this.no == no) {
            return this;
        }
        return resNode;
    }
}

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原文链接：https://www.cnblogs.com/guizimo/p/13451653.html

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