[LeetCode141]Linked List Cycle

题目：Given a linked list, determine if it has a cycle in it.

　　判断一个链表是否有环

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) {
        ListNode *fast(head), *slow(head);
        while(fast && fast->next)
        {
            fast = fast->next->next;
            slow = slow->next;
            if(fast == slow)
                return true;
        }
        return false;
    }
};

关于进一步求环的长度和入口结点可以看另一篇博客http://www.cnblogs.com/zhangbaochong/p/5151986.html