/*
141. Linked List Cycle

First submitted: January 16, 2022
Last submitted: September 30, 2024

Runtime: 11 ms (beats 43.81%)
Memory: 10.70 MB (beats 85.26%)
*/

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