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:
        if head == None or head.next==None:
            return False
        fast=head.next.next
        slow=head.next
        while fast and slow:
            if slow==fast:
                return True
            if fast.next ==None:
                return False
            else:
                slow = slow.next
                fast = fast.next.next
        return False