Linked List Cycle

lc_141.cpp

/**
 * 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) {
        if(head == NULL)
            return false;
        ListNode *step1 = head;
        if(step1->next == NULL)
            return false;
        ListNode *step2 = step1->next;
        
        while(step1!=NULL && step2!=NULL)
        {
            if(step1 == step2)
                return true;
            
            if(step1->next != NULL)
                step1 = step1->next;
            if(step2->next == NULL)
                return false;
            else
                step2 = step2->next->next;
        }
        return false;
    }
};