题解 | #判断链表中是否有环#

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
#include <unordered_map>
class Solution {
public:
    bool hasCycle(ListNode *head) {
        //哈希表
        unordered_map<ListNode *, int> map;
        while(head){
            if(map.count(head)==0)
                map[head]=1;
            else
                return true;
            head=head->next;
        }
        return false;
    }
};