# 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 p1 = head while(head and head.next): p1 = p1.next head = head.next.next if (p1 == head): return True return False