题解 | 判断链表中是否有环

from os import mkdir
# 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: return False
        s=head
        f=head
        while s and f:
            s=s.next
            if f.next:
                f=f.next.next
            else: return False
            if s==f:return True
        return False