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 head==None: return False slow=head fast=head while fast.next!=None and fast.next.next!=None: slow=slow.next fast=fast.next.next if slow is fast: return True return False