[leetcode_141]Linked List Cycle

This problem asks you to determine whether a singly linked list has a cycle, without using extra space.
At first I really didn’t know how to solve it, so I looked at other people’s solutions.
The idea is to use two pointers: one advances one step at a time, the other advances two steps. If they reach NULL without ever being equal, there is no cycle. If they become equal, a cycle exists.
Code below. I honestly feel my pointer and linked list skills are pretty weak.

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

            if(step2 == NULL || step2->next == NULL)
            {
                return false;
            }

            step2 = step2->next->next;

            if(step1 == step2)
            {
                return true;
            }
        }
    }
};