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:
        slow = head
        if slow == None:
            return False
        fast = head.next
        while ((fast != None) & (slow != None)):
            if slow == fast:
                return True
            slow = slow.next
            if fast.next == None:
                return False
            fast = fast.next.next
        return False