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