Question

Given a linked list, determine if it has a cycle in it. 判断链表是否有环

Algorithm

用两个指针，一快一慢，如果它们会在某一个地方相遇则证明有环

Accepted Code

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