题解 | 删除有序链表中重复的元素-II

# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None
#
# 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
#
# 
# @param head ListNode类 
# @return ListNode类
#
class Solution:
    def deleteDuplicates(self , head: ListNode) -> ListNode:
        # write code here
        if not head or not head.next:
            return head
        dummy = ListNode(-1001)
        dummy.next = head#添加哑巴节点，确保头节点和之后的节点处于同样可操作状态
        pre, cur = dummy, head#前一节点，当前节点
        while cur:#当前节点存在
            if cur.next and cur.val==cur.next.val:#当前节点与后一节点重复
                while cur.next and cur.val==cur.next.val:#移动到重复节点最末尾节点
                    cur = cur.next
                pre.next, cur = cur.next, cur.next#删除重复段
            else:
                pre, cur = cur, cur.next
        return dummy.next