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class DoublyListNode {
    int val;
    DoublyListNode prev, next;

    DoublyListNode(int val) {
        this.val = val;
        this.prev = null;
        this.next = null;
    }
}

public class ReverseDoublyLinkedList {

    // Reverse a Doubly Linked List
    public DoublyListNode reverseDLL(DoublyListNode head) {
        if (head == null) return null; // If the list is empty

        DoublyListNode current = head;
        DoublyListNode temp = null;

        // Swap next and prev for all nodes
        while (current != null) {
            temp = current.prev;
            current.prev = current.next;
            current.next = temp;
            current = current.prev; // Move to the next node (which is prev after the swap)
        }

        // After the loop, temp points to the last node, which becomes the new head
        if (temp != null) {
            head = temp.prev; // Update head to the new head
        }

        return head;
    }