141. Linked List Cycle

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/**
 * 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 == NULL){return 0;}
        ListNode *fast = head,*slow = head;
        fast = fast->next;
        while(fast != NULL && fast != slow){
            fast = fast->next;
            if(fast == NULL){return 0;}
            fast = fast->next;
            slow = slow->next;
        }
        if(fast == NULL){return 0;}
        else{return 1;}
    }
};