Convert a Binary Tree to a Circular Doubly Link List

<script>
// javascript Program to convert a Binary Tree to a
// Circular Doubly Linked List

// Node class represents a Node of a Tree
class Node {
    constructor(val) {
        this.val = val;
        this.left = null;
        this.right = null;
    }
}

// A class to represent a 

        var root = null;


    // concatenate both the lists and returns the head
    // of the List
     function concatenate(leftList,  rightList) {
        // If either of the list is empty, then
        // return the other list
        if (leftList == null)
            return rightList;
        if (rightList == null)
            return leftList;

        // Store the last Node of left List
        var leftLast = leftList.left;

        // Store the last Node of right List
        var rightLast = rightList.left;

        // Connect the last node of Left List
        // with the first Node of the right List
        leftLast.right = rightList;
        rightList.left = leftLast;

        // left of first node refers to
        // the last node in the list
        leftList.left = rightLast;

        // Right of last node refers to the first
        // node of the List
        rightLast.right = leftList;

        // Return the Head of the List
        return leftList;
    }

    // Method converts a  to a circular
    // Link List and then returns the head
    // of the Link List
     function bTreeToCList(root) {
        if (root == null)
            return null;

        // Recursively convert left and right subtrees
        var left = bTreeToCList(root.left);
        var right = bTreeToCList(root.right);

        // Make a circular linked list of single node
        // (or root). To do so, make the right and
        // left pointers of this node point to itself
        root.left = root.right = root;

        // Step 1 (concatenate the left list with the list
        // with single node, i.e., current node)
        // Step 2 (concatenate the returned list with the
        // right List)
        return concatenate(concatenate(left, root), right);
    }

    // Display Circular Link List
     function display(head) {
        document.write("Circular Linked List is :<br/>");
        var itr = head;
        do {
            document.write(itr.val + " ");
            itr = itr.right;
        } while (itr != head);
        document.write();
    }


       // Driver Code

    
        // Build the 
        root = new Node(10);
        root.left = new Node(12);
        root.right = new Node(15);
        root.left.left = new Node(25);
        root.left.right = new Node(30);
        root.right.left = new Node(36);

        // head refers to the head of the Link List
        var head = bTreeToCList(root);

        // Display the Circular LinkedList
        display(head);

// This code contributed by umadevi9616
</script>

// A javascript program for in-place conversion of Binary Tree to DLL
// A binary tree node has data, left pointers and right pointers
class Node {
    constructor(val) {
        this.data = val;
        this.left = null;
        this.right = null;
    }
}
var root;

// head --> Pointer to head node of created doubly linked list
var head;

// Initialize previously visited node as NULL. This is
// so that the same value is accessible in all recursive
// calls
var prev = null;

// A simple recursive function to convert a given Binary tree
// to Doubly Linked List
// root --> Root of Binary Tree
function BinaryTree2DoubleLinkedList(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 */
function printList(node) {
    while (node != null) {
        console.log(node.data + " ");
        node = node.right;
    }
}

// Driver program to test above functions
// Let us create the tree as shown in above diagram
root = new Node(10);
root.left = new Node(12);
root.right = new Node(15);
root.left.left = new Node(25);
root.left.right = new Node(30);
root.right.left = new Node(36);

// convert to DLL
BinaryTree2DoubleLinkedList(root);

// Print the converted List
printList(head);

// This code is contributed by ishankhandelwals.