leetcode python3 环形链表

代码思路：利用快慢指针遍历链表，若存在环形链表，两指针必相遇，否则快指针会先遍历完成

class Solution:
    def hasCycle(self, head: ListNode) -> bool:
        show=fast=head
        while fast and fast.next:
            show=show.next
            fast=fast.next.next
            if show==fast:
                return True
        return False