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Answer for doubly link list

18. Reverse the doubly link list.
For ( p = head; p->next != head; p = p->prev )
Swap (&p->next,&p->prev);

19. Doubly link list a single pointer.
While storing the address store address as xor of the previous and next.

20. Reverse the link list with ‘k’ nodes.
Take the k+1 the element pointer and put as the next for first element . Reverse the K sized list .
21. Find a list in palindrome or not.
a) Find the middle node, reverse link list after that. Start comparing from head and the node after the middle node.

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