# Definition for singly-linked list.
class ListNode:
    def __init__(self, x):
        self.val = x
        self.next = None

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None
class Solution:
    def hasCycle(self, head: Optional[ListNode]) -> bool:
        cnt = 0
        if head == None: return False
        while cnt < 1e4+10:
            if head.next == None:
                return False
            head = head.next
            cnt += 1
        return True