LeetCode 141

/**
 * 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) {
   
        unordered_set<ListNode *>store;
        ListNode *t=head;
        while(t)
        {
   
            if(store.count(t))
            {
   
                return true;
            }
            store.insert(t);
            t=t->next;
        }
        return false;
    }
};