题目：
给定一个排序链表，删除所有重复的元素，使得每个元素只出现一次。
示例 1:
输入: 1->1->2
输出: 1->2
示例 2:
输入: 1->1->2->3->3
输出: 1->2->3
class ListNode:
def __init__(self, x):
self.val = x
self.next = None
class Solution:
def deleteDuplicates(self, head: ListNode) -> ListNode:
if head == None or head.next == None:
return head
cur = head
while cur.next:
if cur.val == cur.next.val:
if cur.next.next == None:
cur.next = None
else:
cur.next = cur.next.next
else:
cur = cur.next
return head
