class Solution:

    def deleteDuplicates(self, head: ListNode) -> ListNode:

        if head==None or head.next==None:

            return head

        head.next = self.deleteDuplicates(head.next)

        if head.val==head.next.val:

            head=head.next # python无需像C++一样手动释放内存

return head

class Solution:

    def deleteDuplicates(self, head):

        """

        :type head: ListNode

        :rtype: ListNode

        """

        lb = head

        # while写lb.val就会错？'NoneType' object has no attribute 'val'

        while lb and lb.next:

            if lb.val == lb.next.val:

                lb.next = lb.next.next

            else:

                lb = lb.next

        return head