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 ):
        # write code here
        if not head or head.next == None:
            return False

        # 快慢指针
        fast = slow = head

        while fast and fast.next:

            fast = fast.next.next
            slow = slow.next

            if fast == slow:
                return True

        return False