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||!head->next) return false;
        ListNode* fast = head;
        ListNode* slow = head;
        while(fast&&slow){
            if(fast->next)
            {
                fast = fast->next->next;
            }else{
                return false;
            }
            slow = slow->next;
            if(fast==slow) return true;
        }
        return false;
    }
};