LeetCode:Linked List Cycle

 1 /**
 2  * Definition for singly-linked list.
 3  * struct ListNode {
 4  *     int val;
 5  *     ListNode *next;
 6  *     ListNode(int x) : val(x), next(NULL) {}
 7  * };
 8  */
 9 class Solution {
10     public:
11         bool hasCycle(ListNode *head) {
12             if(head==NULL)
13                 return false;
14             ListNode *p=head,*q;
15             int n=0,m;
16             while(p!=NULL)
17             {
18                 q=head;
19                 m=0;
20                 while(m<=n)
21                 {
22                     if(q==p->next)
23                         return true;
24                     else
25                     {
26                         q=q->next;
27                         m++;
28                     }
29                 }
30                 p=p->next;
31                 n++;
32             }
33             return false;
34         }
35 };