# 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 = head
        fast = head
        
        while fast and fast.next:
            slow = slow.next 
            fast = fast.next.next 
            if slow==fast:
                return True
        return False    
        