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) 
    {
        ListNode* fast = head;
        ListNode* slow = head;
        while(fast != NULL && fast->next != NULL)
        {
            fast = fast->next->next;  //快指每次走两步
            slow = slow->next;        //慢指针每次走一步
            if (fast == slow)
            {
                return true;
            }
        }
        return false;
    }
};