Linked List Cycle 题解

题目来源：Linked List Cycle

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Given a linked list, determine if it has a cycle in it.

解题思路：

简单的快慢指针.

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