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

本质上考察的就是快慢指针，类似于赛马之类的题，重点需要考虑到不同情况下无环的判断条件，因为有各种出现none的情况