Leetcode刷题笔记(c++)

class Solution {
public:
    ListNode *detectCycle(ListNode *head) {
        unordered_sethashset;
        while(head){
            if(hashset.count(head)){
                return head;
            }
            hashset.insert(head);
            head=head->next;
        }
        return NULL;        
    }
};