题目链接: linked List Cycle

题目意思: 给定一个链表，判断链表是否有环

代码:

/**
 * 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);
};

bool Solution::hasCycle (ListNode *head) {
    if (NULL == head) {
        return false;
    }
    ListNode *tmpHeadOne = head;
    ListNode *tmpHeadTwo = head;
    int step = 0;
    while ((tmpHeadOne != NULL) && (tmpHeadTwo != NULL)) {
        if ((step != 0) && (tmpHeadOne == tmpHeadTwo)) {
            return true;
        }
        step++;
        tmpHeadOne = tmpHeadOne->next;
        tmpHeadTwo = tmpHeadTwo->next;
        if (tmpHeadTwo != NULL) {
            tmpHeadTwo = tmpHeadTwo->next;
        }
    }
    return false;
}