public bool IsPalindrome(ListNode head) {         if(head == null) return true;         ListNode slow = head;         ListNode fast = head;         ListNode nextNode = null;         ListNode newHead = null;                  //get middle pointer of the linked list         while(fast != null && fast.next != null)         {             slow = slow.next;             fast = fast.next.next;         }                   while(slow != null)             {                 nextNode = slow.next;                 slow.next = newHead;                 newHead = slow;                 slow = nextNode;             }         while(head != null && newHead != null)         {             if(head.val != newHead.val) return false;             head = head.next;             newHead = newHead.next;         }         return true;     }