clean python solution involving dummy node
```\nclass Solution(object):\n    def deleteDuplicates(self, head):\n        """\n        :type head: ListNode\n        :rtype: ListNode\n        """\n        d
```\nclass Solution(object):\n    def deleteDuplicates(self, head):\n        """\n        :type head: ListNode\n        :rtype: ListNode\n        """\n        dummy = ListNode(-1)\n        dummy.next = head\n        prev, curr = dummy, dummy.next\n        \n        while curr:\n            if curr.next and curr.val == curr.next.val:\n                val_to_rem = curr.val\n                \n                while curr and curr.val == val_to_rem:\n                    curr = curr.next\n                    \n                prev.next = curr\n                \n            else:\n                prev, curr = curr, curr.next\n                \n        return dummy.next
[]