1. 题目
Given a linked list, determine if it has a cycle in it.
Follow up:Can you solve it without using extra space?
2.解决方案
class Solution {public:bool hasCycle(ListNode *head) {if(!head){return false;}ListNode* slowPoint = head;ListNode* fastPoint = head;while(slowPoint->next){//slow point move one stepslowPoint = slowPoint->next;//fast point move two stepif(fastPoint->next){fastPoint = fastPoint->next;}else{return false;}if(fastPoint->next){fastPoint = fastPoint->next;}else{return false;}if(slowPoint->val == fastPoint->val){return true;}}return false;}};
思路：用快慢指针来走，如果有环的话，，一定会遇到一起。
如果你曾歌颂黎明，那么也请你拥抱黑夜
