Leetcode 141. Linked List Cycle

https://leetcode.com/problems/linked-list-cycle/

For this problem, the best solution is to use two pointers: slow and fast. If they meet at somewhere, there is a cycle.

Solution:

# T:O(n) S:O(1)
class Solution:
    # @param head, a ListNode
    # @return a boolean
    def hasCycle(self, head):
        fast, slow = head, head
        while fast and fast.next:
            fast, slow = fast.next.next, slow.next
            if fast is slow:
                return True
        return False

Run Time: 76 ms