[Linked List]Linked List Cycle,Linked List Cycle II

/**
 * 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 || head->next==NULL){
            return false;
        }
        ListNode *first =head;
        ListNode *second = head;
        while(first && second)
        {
            first = first->next;
            second = second->next;
            if(second){
                second = second->next;
            }
            if(first==second){
                return true;
            }
        }
        return false;
    }
};