Java Program to Implement Double Order Traversal of a Binary Tree

Code:

import java.util.Scanner;

class BinarySearchTreeNodes
{
    BinarySearchTreeNodes left, right;
    int      data;

    public BinarySearchTreeNodes()
    {
        left = null;
        right = null;
        data = 0;
    }

    public BinarySearchTreeNodes(int n)
    {
        left = null;
        right = null;
        data = n;
    }

    public void setLeft(BinarySearchTreeNodes n)
    {
        left = n;
    }

    public void setRight(BinarySearchTreeNodes n)
    {
        right = n;
    }

    public BinarySearchTreeNodes getLeft()
    {
        return left;
    }

    public BinarySearchTreeNodes getRight()
    {
        return right;
    }

    public void setData(int d)
    {
        data = d;
    }

    public int getData()
    {
        return data;
    }
}

class BinarySearchTree
{
    private BinarySearchTreeNodes root;

    public BinarySearchTree()
    {
        root = null;
    }

    public boolean isEmpty()
    {
        return root == null;
    }

    public void insert(int data)
    {
        root = insert(root, data);
    }

    private BinarySearchTreeNodes insert(BinarySearchTreeNodes node, int data)
    {
        if (node == null)
            node = new BinarySearchTreeNodes(data);
        else
        {
            if (data <= node.getData())
                node.left = insert(node.left, data);
            else
                node.right = insert(node.right, data);
        }
        return node;
    }

public void doubleorder()
{
doubleorder(root);
}

private void doubleorder(BinarySearchTreeNodes r)
{
if(r != null)
{
System.out.print(r.getData() + " ");
doubleorder(r.getLeft());
System.out.print(r.getData() + " ");
doubleorder(r.getRight());
}
}
}

public class Doubleorder_Traversal
{
    public static void main(String[] args)
    {
        Scanner scan = new Scanner(System.in);
        BinarySearchTree bst = new BinarySearchTree();
        System.out.println("Enter the first 10 elements of the tree\n");
        int N = 10;
        for (int i = 0; i < N; i++)
            bst.insert(scan.nextInt());

        System.out.print("\nDouble-order   : ");
        bst.doubleorder();

        scan.close();
    }
}


Output:

Enter the first 10 elements of the tree

12 10 11 03 15 19 02 01 04 70

Double-order   : 12 10 3 2 1 1 2 3 4 4 10 11 11 12 15 15 19 19 70 70



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