题目：
Given a linked list, determine if it has a cycle in it.
Example
Given -21->10->4->5, tail connects to node index 1, return true
题解：
Solution 1 ()
class Solution { public: bool hasCycle(ListNode *head) { if (!head) { return false; } ListNode* fast = head; ListNode* slow = head; while (fast && fast->next) { slow = slow->next; fast = fast->next->next; if (slow == fast) { return true; } } return false; } };
【Lintcode】102.Linked List Cycle
原文：http://www.cnblogs.com/Atanisi/p/6848373.html