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) {
        ListNode* tp1 = head;
        ListNode* tp2 = head;
        while(tp2 != NULL && tp2->next != NULL){
            tp1 = tp1->next;
            tp2 = tp2->next->next;
            if(tp1 == tp2){
                return true;
            }
        }
        return false;
    }
};