【leetcode】82. 删除排序链表中的重复元素 II（python）

注意：head也有可能被删除，所以设置个哑变量dummy指向head，统一操作。

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def deleteDuplicates(self, head: ListNode) -> ListNode:
        if not head or not head.next:
            return head
        dummy = ListNode(-101, head)
        pre, cur = dummy, head
        repeated = -101
        while cur.next:
            nxt = cur.next
            if cur.val == nxt.val or cur.val == repeated:
                pre.next = nxt
                repeated = cur.val
                cur = nxt
            else:
                pre = cur
                cur = cur.next
        if cur.val == repeated:
            pre.next = None
        return dummy.next