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
#
# 像这种题，在结束循环的时候一定要加一个 ans.next = None 以终止链表
class Solution:
    def deleteDuplicates(self , head: ListNode) -> ListNode:
        if head == None or head.next == None:
            return head

        preValue = head.val-1
        ans = ListNode(0)
        ansNode = ans

        while head.next != None:
            if head.val != preValue and head.val != head.next.val:
                ans.next = head
                ans = ans.next
            preValue = head.val
            head = head.next
        if head.val != preValue:
            ans.next = head
            ans = ans.next
        ans.next = None
        return ansNode.next