leetcode - Linked List Cycle

 

/**
 * 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) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        ListNode * itr = head;
        int n = 1;
        while (true){
            if (itr==NULL)
                return false;
            ListNode * tmp = itr;
            for (int i=0; i<n; i++){
                tmp = tmp->next;
                if (tmp==NULL)
                    return false;
                else if (tmp == itr)
                    return true;
            }
            n++;
            itr = itr->next;
        }
        return false;
    }
};