Linked List Cycle.py

from typing import Optional


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


class Solution:
    """
    Time:   O(n)
    Memory: O(1)
    """

    def hasCycle(self, head: Optional[ListNode]) -> bool:
        fast = head
        slow = head

        while fast and fast.next:
            slow = slow.next
            fast = fast.next.next
            if slow == fast:
                return True

        return False