LeetCode 141. Linked List Cycle

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

Follow up: Can you solve it without using extra space?

思路： 判断一个链表中是否有循环，运用快慢指针，如果有循环，肯定会相遇

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 *slow = head; ListNode *fast = head; while(fast != NULL && fast->next != NULL){//用快慢指针方法，如果有循环 fast = fast->next->next; if(fast == slow){//则一定存在相遇情况 return true; } } return false; } };