题解 | #判断链表中是否有环#

from math import fabs
# 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 is None or head.next is None:
            return False
        slow, fast = head, head.next
        while fast and fast.next:
            if slow == fast:
                return True
            fast = fast.next.next
            slow = slow.next

        return False

使用快慢指针即可，注意while的条件中要判断fast.next也非空