题解 | #判断链表中是否有环#

import re
#     def __init__(self, x):
#         self.val = x
#         self.next = None

#
# 
# @param head ListNode类 
# @return bool布尔型
#
class Solution:
    def hasCycle(self , head: ListNode) -> bool:
        if not head:
            return False
        if head.next is None:
            return False
        slow = head
        fast = slow
        while fast and slow:
            slow = slow.next
			# 判断是否有环 无环直接false
            if fast.next:
                fast = fast.next.next
            else:
                return False
            if slow == fast:
                return True
	#   fast或者slow为None
        return False