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) {}
 * };
 */
class Solution {
public:
    bool hasCycle(ListNode *head) {
        if(head==nullptr) return false;

        ListNode *l=head;
        ListNode *r=head;

        while(r && r->next){
            r=r->next->next;

           l=l->next;

            if(l==r){
                return true;
            }
        }

        return false;

    }
};