[leetcode] 【链表】141. Linked List Cycle

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

Follow up:

Can you solve it without using extra space?

题意

 判断一个链表是否是循环链表。

题解

 射两个指针，一快一慢，如果快的套了慢的一圈，那么就是循环的，

快的到了尾，那么就是不循环的。

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