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;
}
};