力扣第141题 环形链表

力扣第141题 环形链表

/**
 * 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 || head->next == NULL)
        {
            return false;
        }
        ListNode * stepOne = head;
        ListNode * stepTwo = head->next;
        while (stepOne != stepTwo)
        {
            if (stepTwo == NULL || stepTwo->next == NULL)
            {
                return false;
            }
            stepOne = stepOne->next;
            stepTwo = stepTwo->next->next;
        }
        return true;
    }
};