题解 | 判断链表中是否有环,空间换时间

# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

#
# 
# @param head ListNode类 
# @return bool布尔型
#
class Solution:
    def __init__(self) -> None:
        self.hashset = set()
    def hasCycle(self , head: ListNode) -> bool:
        p = head
        while p is not None:
            if id(p) in self.hashset:
                return True
            else:
                self.hashset.add(id(p))
            p = p.next
        return False