题解 | #判断链表中是否有环# | C++

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