Leetcode_num7_Linked List Cycle

题目：

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

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

这是一道关于链表比较简单的题，很顺利就解决了，不多说啦，上代码啦

# Definition for singly-linked list.# class ListNode:#     def __init__(self, x):#         self.val = x#         self.next = Noneclass Solution:    # @param head, a ListNode    # @return a boolean    def hasCycle(self, head):        if head==None:            check=False        else:            check=True            node=head            while(node.val!=0):                node.val=0                node=node.next                if node==None:                    check=False                    break        return check