腾讯精选32--python

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
    def hasCycle(self, head):
        """
        :type head: ListNode
        :rtype: bool
        """
        if head==None:
            return False
        slow,fast=head,head.next
        if fast==None:
            return False
        while slow!=fast:
            if fast.next==None:
                return False
            elif fast.next.next==None:
                return False                
            slow=slow.next
            fast=fast.next.next
        return True

还是双指针方法灵活

来源：https://blog.csdn.net/weixin_45569078/article/details/101036155