【leetcode】Linked List Cycle

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?

本题是链表的题目，注意链表的具体表达~~用双指针来实现

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