rekt.cpp

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode *detectCycle(ListNode *head) {
        if (!head) return NULL;
        
        map<ListNode*, int> nodes = map<ListNode*, int>();
        while (head->next) { 
            try {
                if (nodes.at(head->next) == 0) return head->next;
            }
            catch (out_of_range o) {
                nodes.insert(pair<ListNode*, int>(head, 0));
                head = head->next;
            }
        }
        
        return NULL;
    }
};