[LeedCode OJ]#141 Linked List Cycle

/**
 * 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)
    {
        if(head==NULL)
            return false;
        ListNode *fast,*slow;
        fast = slow = head->next;
        while(fast!=NULL&&fast->next!=NULL)
        {
            fast = fast->next->next;
            slow = slow->next;
            if(fast==slow)
                return true;
        }
        return false;
    }
};