in-place conversion of Binary Tree to DLL

BTtoDLL.java

// A Java program for in-place conversion of Binary Tree to DLL
class Node 
{
    int data;
    Node left, right;

    public Node(int data) 
    {
        this.data = data;
        left = right = null;
    }
}

class BinaryTree 
{
    Node root;
    
    // head --> Pointer to head node of created doubly linked list
    Node head;
    
    // Initialize previously visited node as NULL. This is
    // static so that the same value is accessible in all recursive
    // calls
    Node prev = null;

    // A simple recursive function to convert a given Binary tree 
    // to Doubly Linked List
    // root --> Root of Binary Tree
    void BinaryTree2DoubleLinkedList(Node root) 
    {
        // Base case
        if (root == null)
            return;

        // Recursively convert left subtree
        BinaryTree2DoubleLinkedList(root.left);

        // Now convert this node
        if (prev == null) 
            head = root;
        else
        {
            root.left = prev;
            prev.right = root;
        }
        prev = root;

        // Finally convert right subtree
        BinaryTree2DoubleLinkedList(root.right);
    }

    /* Function to print nodes in a given doubly linked list */
    void printList(Node node)
    {
        while (node != null) 
        {
            System.out.print(node.data + " ");
            node = node.right;
        }
    }

    // Driver program to test above functions
    public static void main(String[] args) 
    {
        // Let us create the tree as shown in above diagram
        BinaryTree tree = new BinaryTree();
        tree.root = new Node(10);
        tree.root.left = new Node(12);
        tree.root.right = new Node(15);
        tree.root.left.left = new Node(25);
        tree.root.left.right = new Node(30);
        tree.root.right.left = new Node(36);

        // convert to DLL
        tree.BinaryTree2DoubleLinkedList(tree.root);
        
        // Print the converted List
        tree.printList(tree.head);

    }
}