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
#
#如果有环则返回true，否则返回false。
class Solution:
    def hasCycle(self , head: ListNode) -> bool:
        if head is None:
            return False
        Phead=head
        fast=head
        slow=head
        while fast is not None and fast.next is not None:
            fast=fast.next.next
            slow=slow.next
            if fast==slow:
                return True
        else:
            return False