linked-list-cycle

题目描述
Given a linked list, determine if it has a cycle in it.
Follow up:

Can you solve it without using extra space?

IDEA

借助 点击打开链接

缓慢指针能相遇，说明有环

CODE

/** * 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 false;        ListNode *slow=head,*fast=head;        while(fast&&fast->next){            slow=slow->next;            fast=fast->next->next;            if(slow==fast)                return true;        }        return false;    }};