题解 | #删除有序链表中重复的元素-I#

# 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
        # 用集合实现
        if not(head):
            return head
        visit = {head.val}
        pre = head
        this = head.next
        while this:
            if this.val in visit:
                pre.next = this.next
                this = this.next
            else:
                visit.add(this.val)
                pre = this
                this = this.next
        return head