题解 | #判断链表中是否有环#

# class ListNode:

# from numpy.random import f
#     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
        slow=head
        fast=head

        while fast.next and fast.next.next:
            slow=slow.next
            fast=fast.next.next
            if slow==fast:
                return True
        return False