[leetcode]141. Linked List Cycle

题目链接：https://leetcode.com/problems/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?

class Solution {public:    bool hasCycle(ListNode *head)                {                        ListNode *slow=head,*fast=head;                                                while(fast!=NULL && fast->next!=NULL)                        {                                                                slow=slow->next;                                fast=fast->next->next;                                if(slow==fast)                                        return true;                        }                        return false;                }};