LeetCode 82. 删除排序链表中的重复元素 II

给定一个排序链表，删除所有含有重复数字的节点，只保留原始链表中?没有重复出现?的数字。

示例?1:
输入: 1->2->3->3->4->4->5
输出: 1->2->5

示例?2:
输入: 1->1->1->2->3
输出: 2->3

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    def deleteDuplicates(self, head: ListNode) -> ListNode:
        if head is None or head.next is None:
            return head 
        node = ListNode(None)
        node.next = head 
        pre = node 
        cur = head 
        while cur is not None and cur.next is not None:
            if cur.val == cur.next.val:
                while cur.next is not None and cur.val == cur.next.val:
                    cur = cur.next 
                pre.next = cur.next 
                cur = cur.next 
            else:
                cur = cur.next 
                pre = pre.next 
        return node.next