反转循环双向链表

Question

I'm attempting to implement a reverse() function on a circular doubly linked list.

Here is my code:

public void reverseCDLL() {

    if (head != null) {

       Node current = head, next, temp;

       do{

           next = current.getNextNode();
           temp = current.getPrevNode();
           current.setPrevNode(current.getNextNode());
           current.setNextNode(temp);
           current = next;

       }while(current != head);
    }
}

Input: 1 2 3 4

Output: 1 4 3 2

Expected Output: 4 3 2 1

I'm very close to finishing this but one little thing is wrong and I just can't pin point what it is.

Any assistance / hints would be greatly appreciated.

Answer 1

The algorithm works fine, you just need to change the head pointer to the correct value. When you reverse a linked list the head points to the last node, similarly in this case too the head should point to the last node.

public void reverseCDLL() {

    if (head != null) {

       Node current = head, next, temp;

       do{

           next = current.getNextNode();
           temp = current.getPrevNode();
           current.setPrevNode(current.getNextNode());
           current.setNextNode(temp);
           current = next;

       }while(current != head);
       head = head.getNextNode();
    }
}