# Definition for singly-linked list.
# class ListNode:
# def __init__(self, x):
# self.val = x
# self.next = None
class Solution:
def hasCycle(self, head: ListNode) -> bool:
slow = fast = head
while fast is not None and fast.next is not None:
slow = slow.next
fast = fast.next.next
if slow is fast:
return True
return False
