线索二叉树（threaded binary search tree) C#

最新推荐文章于 2023-06-06 12:19:00 发布
zen_chou
最新推荐文章于 2023-06-06 12:19:00 发布
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文章标签： search tree c# traversal null string
本文链接：https://blog.youkuaiyun.com/zen_chou/article/details/3010047
本文介绍了一种特殊的二叉搜索树——线程二叉搜索树(Threaded Binary Search Tree)的实现方法，包括插入、删除操作及中序遍历等核心功能。
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using System;
namespace ThreadedBinaryTree
{
    class Node
    {
        public Node lchild;
        public int lthread;//0 represent a thread,1 represent a link
        public int data;
        public Node rchild;
        public int rthread;
        public Node(int Data,int Lthread,int Rthread,Node Lchild,Node Rchild)
        {
            data = Data;
            lchild = Lchild;
            rchild = Rchild;
            lthread = Lthread;
            rthread = Rthread;
        }
    }
    class ThreadedBST
    {
        private Node head;
        public ThreadedBST()//Constructor
        {
            head = new Node(0, 0, 1, null, null);
            head.lchild = head;
            head.rchild = head;
        }
        public void find(int element, ref Node parent, ref Node currentNode)
        {
            if (head.lthread != 0)//tree is not empty
            {
                currentNode = head.lchild;//the top element of the tree
                parent = head;
                while (currentNode != null && currentNode.data != element)
                {
                    parent = currentNode;
                    if (element < currentNode.data && currentNode.lthread == 1)
                        currentNode = currentNode.lchild;
                    else if (element < currentNode.data && currentNode.lthread == 0)//reach the leaf node of left subtree
                        currentNode = null;
                    else if (element > currentNode.data && currentNode.rthread == 1)
                        currentNode = currentNode.rchild;
                    else if (element > currentNode.data && currentNode.rthread == 0)//reach the leaf node of right subtree
                        currentNode = null;
                }
            }
            else//tree is empty
            {
                parent = head;
                Console.WriteLine("Tree is empty");
            }
        }
        public void insert(int element)
        {
            Node newNode, currentNode=null, parent=null;
            find(element,ref parent,ref currentNode);
            if (currentNode != null)
                return;
            newNode = new Node(element, 0, 0, null, null);
            if (parent != head)//if tree is not empty
            {
                if (element < parent.data)
                {
                    newNode.lchild = parent.lchild;
                    newNode.rchild = parent;
                    parent.lthread = 1;
                    parent.lchild = newNode;
                }
                else if (element > parent.data)
                {
                    newNode.rchild = parent.rchild;
                    newNode.lchild = parent;
                    parent.rthread = 1;
                    parent.rchild = newNode;
                }
            }
            else//if tree is empty
            {
                head.lthread = 1;
                head.lchild = newNode;
                newNode.lchild = newNode.rchild = head;
            }
        }
        //if the right child of the node is a link, then we can traverse to the leftmost node in the 
        //right subtree of that node to find its inorder successor.However, if the right child of the 
        //node is a thread, then the thread will point to the inorder successor of that node
        public Node Inorder_successor(ref Node currentNode)//search the successor of currentNode
        {
            Node inorder_current=null;
            if (currentNode.rthread == 0)
            {//if the right child of currentNode is a thread,then the node which the thread point to is successor
                return currentNode.rchild;
            }
            inorder_current = currentNode.rchild;//make currentNode point to the right child of currentNode
            while (inorder_current.lthread != 0)//loop until reach the leaf node of left subtree
                inorder_current  = inorder_current.lchild;
            return inorder_current;
        }
        public Node Inorder_predecessor(ref Node currentNode)//search the predecessor of currentNode
        {
            Node inorder_current = null;
            if (currentNode.lthread == 0)
                return currentNode.lchild;
            inorder_current = currentNode.lchild;
            while (inorder_current.rthread != 0)
                inorder_current = inorder_current.rchild;
            return inorder_current;
        }
        public void Inorder_traversal()
        {
            Node currentNode;
            if (head.lthread == 0)
            {
                Console.WriteLine("Tree is empty");
                return;
            }
            currentNode = head.lchild;
            while (currentNode.lthread != 0)//the fist-visit node is the leftmost node of the tree
                currentNode = currentNode.lchild;
            Console.Write(currentNode.data + "   ");
            while (currentNode.rchild != head)
            {
                currentNode = Inorder_successor(ref currentNode);
                Console.Write(currentNode.data + "   ");
            }
        }
        public void delete(int element)
        {
            Node parent=null, currentNode=null, child=null, successor=null, predecessor=null, inorder_parent=null;
            find(element, ref parent, ref currentNode);
            if (currentNode != null)
            {
                successor = Inorder_successor(ref currentNode);
                predecessor = Inorder_predecessor(ref currentNode);
                if (currentNode.lthread == 0 && currentNode.rthread == 0)//node to be deleted is a leaf node
                {
                    if (parent != head)
                    {
                        if (parent.lchild == currentNode)
                        {
                            parent.lthread = 0;
                            parent.lchild = currentNode.lchild;
                        }
                        else
                        {
                            parent.rthread = 0;
                            parent.rchild = currentNode.rchild;
                        }
                    }
                    else
                    {
                        head.lthread = 0;
                        head.lchild = head;
                    }
                }
                else if ((currentNode.lthread == 0 && currentNode.rthread != 0)
                    || (currentNode.lthread != 0 && currentNode.rthread == 0))
                //node to be deleted has one child
                {
                    if (currentNode.lthread == 1)//if currentNode has a left child
                    {
                        child = currentNode.lchild;
                        if (parent.lchild == currentNode)//if currentNode is the left child of parent
                            parent.lchild = child;
                        else
                            parent.rchild = child;
                        predecessor.rchild = successor;
                        predecessor.rthread = 0;
                    }
                    else//current has a right child
                    {
                        child = currentNode.rchild;
                        if (parent.lchild == currentNode)
                            parent.lchild = child;
                        else
                            parent.rchild = child;
                        successor.lchild = predecessor;
                        successor.lthread = 0;
                    }
                }
                else if (currentNode.lthread == 1 && currentNode.rthread == 1)
                {//node to be delete has two children
                    find(successor.data, ref parent, ref successor);
                    inorder_parent = parent;//the parent of successor
                    currentNode.data = successor.data;
                    currentNode = successor;//now delete the successor ,make currentNode point to the successor
                    if (currentNode.lthread == 0 && currentNode.rthread == 0)//node to be deleted is a leaf node
                    {
                        if (parent != head)
                        {
                            if (parent.lchild == currentNode)
                            {
                                parent.lthread = 0;
                                parent.lchild = currentNode.lchild;
                            }
                            else
                            {
                                parent.rthread = 0;
                                parent.rchild = currentNode.rchild;
                            }
                        }
                        else
                        {
                            head.lthread = 0;
                            head.lchild = head;
                        }
                    }
                    if ((currentNode.lthread == 0 && currentNode.rthread != 0)
                        || (currentNode.lthread != 0 && currentNode.rthread == 0))
                    //node to be deleted has one child
                    {
                        if (currentNode.lthread == 1)//if currentNode has a right child
                        {
                            child = currentNode.lchild;
                            if (parent.lchild == currentNode)//if currentNode is the left child of parent
                                parent.lchild = child;
                            else
                                parent.rchild = child;
                            successor.lchild = predecessor;
                            successor.lthread = 0;
                        }
                        else//current has a left child
                        {
                            child = currentNode.rchild;
                            if (parent.lchild == currentNode)
                                parent.lchild = child;
                            else
                                parent.rchild = child;
                            successor.lchild = predecessor;
                            successor.rthread = 0;
                        }
                    }
                }
            }
        }
        static void Main(string[] args)
        {
            ThreadedBST b = new ThreadedBST();
            while (true)
            {
                Console.Clear();
                Console.Write("Inorder traverse:");
                b.Inorder_traversal();
                Console.WriteLine("/nMenu");
                Console.WriteLine("1. Implement insert operation");
                Console.WriteLine("2. Implement delete operation");
                Console.WriteLine("3. Exit");
                Console.Write("/nEnter your Choice:");
                char ch = Convert.ToChar(Console.ReadLine());
                switch (ch)
                {
                    case '1':
                        {
                            Console.Write("Enter a number: ");
                            int num =Convert.ToInt32( Console.ReadLine());
                            b.insert(num);
                        }
                        break;
                    case '2':
                        {
                            Console.Write("Enter a number: ");
                            int num =Convert.ToInt32( Console.ReadLine());
                            b.delete(num);
                        }
                        break;
                    case '3':
                        return;
                    default:
                        Console.WriteLine("Invalid option");
                        break;
                }
            }
        }
    }
}