leetcode_c++：链表：Linked List Cycle(141)

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

---

O（n）

---

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