programming-examples/java/Searching_Sorting_Algorithms/Java Program to Implement Multi-Threaded Version of Binary Search Tree.java

/*This is a Java Program to implement Threaded Binary Tree.
A threaded binary tree makes it possible to traverse the values in the binary tree via a linear traversal that is more rapid than a recursive in-order traversal.
It is also possible to discover the parent of a node from a threaded binary tree, without explicit use of parent pointers or a stack, albeit slowly.
This can be useful where stack space is limited, or where a stack of parent pointers is unavailable (for finding the parent pointer via DFS).*/

//This is a java program to search an element in a multi-threaded version of binary search tree
import java.util.Scanner;

class TBSTNode
{
    int ele;
    TBSTNode left, right;
    boolean leftThread, rightThread;

    public TBSTNode(int ele)
    {
        this(ele, null, null, true, true);
    }

    public TBSTNode(boolean leftThread, boolean rightThread)
    {
        this.ele = Integer.MAX_VALUE;
        this.left = this;
        this.right = this;
        this.leftThread = leftThread;
        this.rightThread = rightThread;
    }

    public TBSTNode(int ele, TBSTNode left, TBSTNode right, boolean leftThread, boolean rightThread)
    {
        this.ele = ele;
        this.left = left;
        this.right = right;
        this.leftThread = leftThread;
        this.rightThread = rightThread;
    }
}

class ThreadedBinarySearchTree
{
    private TBSTNode root;
    public ThreadedBinarySearchTree ()
    {
        root = new TBSTNode(true, false);
    }

    public void clear()
    {
        root = new TBSTNode(true, false);
    }

    public void insert(int ele)
    {
        TBSTNode ptr = findNode(root, ele);
        if (ptr == null)
            return;
        if (ptr.ele < ele)
            {
                TBSTNode nptr = new TBSTNode(ele, ptr, ptr.right, true, true);
                ptr.right = nptr;
                ptr.rightThread = false;
            }
        else
            {
                TBSTNode nptr = new TBSTNode(ele, ptr.left, ptr, true, true);
                ptr.left = nptr;
                ptr.leftThread = false;
            }
    }

    public TBSTNode findNode(TBSTNode r, int ele)
    {
        if (r.ele < ele)
            {
                if (r.rightThread)
                    return r;
                return findNode(r.right, ele);
            }
        else if (r.ele > ele)
            {
                if (r.leftThread)
                    return r;
                return findNode(r.left, ele);
            }
        else
            return null;
    }

    public boolean search(int ele)
    {
        return findNode(root, ele) == null;
    }

    public void inOrder()
    {
        TBSTNode temp = root;
        for (;;)
            {
                temp = insucc(temp);
                if (temp == root)
                    break;
                System.out.print(temp.ele +" ");
            }
    }

    public TBSTNode insucc(TBSTNode tree)
    {
        TBSTNode temp;
        temp = tree.right;
        if (!tree.rightThread)
            while (!temp.leftThread)
                temp = temp.left;
        return temp;
    }
}

public class Threaded_BST
{
    public static void main(String[] args)
    {
        Scanner scan = new Scanner(System.in);
        ThreadedBinarySearchTree tbst = new ThreadedBinarySearchTree();
        System.out.println("Multi-threaded Binary Search Tree \n");
        char ch;
        do
            {
                System.out.println("\nThreaded Binary Search Tree Operations\n");
                System.out.println("1. insert ");
                System.out.println("2. search");
                System.out.println("3. clear");
                int choice = scan.nextInt();
                switch (choice)
                    {
                    case 1 :
                        System.out.println("Enter integer element to insert");
                        tbst.insert( scan.nextInt() );
                        break;
                    case 2 :
                        System.out.println("Enter integer element to search");
                        System.out.println("Search result : "+ tbst.search( scan.nextInt() ));
                        break;
                    case 3 :
                        System.out.println("\nTree Cleared\n");
                        tbst.clear();
                        break;
                    default :
                        System.out.println("Wrong Entry \n ");
                        break;
                    }
                System.out.print("\nTree = ");
                tbst.inOrder();
                System.out.println();
                System.out.println("\nDo you want to continue (Type y or n) \n");
                ch = scan.next().charAt(0);
            }
        while (ch == 'Y'|| ch == 'y');
        scan.close();
    }
}

/*

Multi-threaded Binary Search Tree

Threaded Binary Search Tree Operations

1. insert
2. search
3. clear
1
Enter integer element to insert
23

Tree = 23

Do you want to continue (Type y or n)

y

Threaded Binary Search Tree Operations

1. insert
2. search
3. clear
1
Enter integer element to insert
867

Tree = 23 867

Do you want to continue (Type y or n)

y

Threaded Binary Search Tree Operations

1. insert
2. search
3. clear
1
Enter integer element to insert
3

Tree = 3 23 867

Do you want to continue (Type y or n)

y

Threaded Binary Search Tree Operations

1. insert
2. search
3. clear
2
Enter integer element to search
45
Search result : false

Tree = 3 23 867

Do you want to continue (Type y or n)