Linked List cycle.cpp

/**
 * 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 || head==NULL)
            return false;
        
        ListNode* temp= head;
        ListNode* temp1 = head;
        while(temp && temp1 &&temp1->next && temp1->next->next){
            temp = temp->next;
            temp1 = temp1->next->next;
            if(temp == temp1){
                return true;
            }
        }
        return false;
    }
};