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 *pSlow = head;
        ListNode *pFast = head;

	  	// 注意这里快慢指针的条件
        while (pFast && pFast->next) {
            pSlow = pSlow->next;
            pFast = pFast->next->next;

            if (pSlow == pFast) {
                return true;
            }
        }
        return false;
    }
};