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:
        p1=head
        p2=head
        while p2 is  not None and p2.next is not None:
            p1=p1.next
            p2=p2.next.next
            if p1==p2:
                return True
        return False