/**

 * Definition for singly-linked list.

 * struct ListNode {

 *     int val;

 *     ListNode *next;

 *     ListNode(int x) : val(x), next(NULL) {}

 * };

 */

class Solution {

public:

    bool hasCycle(ListNode *head) {

        // IMPORTANT: Please reset any member data you declared, as

        // the same Solution instance will be reused for each test case.

		if(!head||!head->next) return false;

		ListNode *p=head;

		ListNode *q=p->next;

		while(q&&q->next)

		{

			if(p==q) return true;

			else

			{

				q=q->next->next;

				p=p->next;

			}

		}

        return false;

    }

};