题解 | #删除有序链表中重复的元素-II#

class Solution:
    def deleteDuplicates(self , head: ListNode) -> ListNode:
        # write code here
        if not head:
            return head
        
        dummy = ListNode(-1)
        dummy.next = head
        ans = dummy
        while ans.next and ans.next.next:
            if ans.next.val == ans.next.next.val:
                tmp = ans.next.val
                ans.next = ans.next.next.next
                while ans.next and ans.next.val == tmp:
                    ans.next = ans.next.next

            else:
                ans = ans.next
        return dummy.next