public void deleteDupNodeInPlace(ListNode head){
        if(head == null) return;

        ListNode current = head;

        while(current != null){
            ListNode runner = current;
            while(runner.next!=null){
                if(current.val == runner.next.val)
                    runner.next = runner.next.next;
                runner = runner.next;
            }
            current = current.next;
        }

    }