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:
        fast = head
        slow = head
        while fast is not None:
            fast = fast.next
            if fast is None:
                return False
            fast = fast.next
            slow = slow.next
            if fast is slow:
                return True
        return False