# [141\. Linked List Cycle](https://leetcode.com/problems/linked-list-cycle/)

:::spoiler Solution

/**
 * 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 && fast->next)
        {
            slow = slow->next;
            fast = fast->next->next;
            if (slow == fast) return true;
        }
        return false;
    }
};

- T: $O(N)$
- S: $O(1)$
:::