LinkedList cycle 1

class Solution {
public:
    bool hasCycle(ListNode *head) {

        unordered_set<ListNode*> s;

        while(head!=NULL){

            if(s.find(head)==s.end()){
                s.insert(head);
            }
            else{
                return true;
            }
            head = head->next;


        }

        return false;

    }
};