Linked List Cycle

Given a linked list, determine if it has a cycle in it.

Follow up: Can you solve it without using extra space?

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

class Solution(object):
    def hasCycle(self, head):
        """
        :type head: ListNode
        :rtype: bool
        """
        if not head:
            return False
        slow = head
        fast = head.next
        while slow and fast:
            if slow == fast:
                return True
            slow = slow.next
            if fast.next:
                fast = fast.next.next
            else:
                return False
        return False

Trick:

def hasCycle(self, head):
    try:
        slow = head
        fast = head.next
        while slow is not fast:
            slow = slow.next
            fast = fast.next.next
        return True
    except:
        return False