linkedListCycle

//141
struct ListNode {
    int val;
    ListNode *next;
    ListNode(int x) : val(x), next(NULL) {}
};

class Solution {
public:
    bool hasCycle(ListNode *head) {
        if(head == nullptr || head->next == nullptr) {
            return(false);
        }

        // can't use a set b/c values aren't unique
        ListNode* slow = head;
        ListNode* fast = head->next;

        while(slow != fast) {
            if(fast == nullptr || fast->next == nullptr) {
                return(false);
            }
            slow = slow->next;
            fast = fast->next->next;
        }
        return(true);
    }
};