题解 | #判断链表中是否有环#

# class ListNode:
#     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:
        slow = head
        fast = head
        while fast and fast.next: #对于不存在环的列表，需要判断fast.next是否存在
            slow = slow.next
            fast = fast.next.next
            if fast == slow:
                return True
        return False