/**
 * 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) {
        if(head==nullptr || head->next==nullptr) return false;
        ListNode *left = head;
        ListNode *right = head;
        while(left!=nullptr && right !=nullptr && right->next!= nullptr)
        {
            left = left->next;
            right = right->next->next;
            if(left == right) return true;
        }
        return false;
    }
};

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