题目

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

Follow up:

Can you solve it without using extra space?

分析

判断链表是否有环,采用快慢指针,如果相遇则表示有环

AC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) {

        if(!head || !head->next){

            return false;

        }

        ListNode* slow = head;

        ListNode* fast = head->next;

        while(fast->next && fast->next->next && fast != slow){

            fast = fast->next->next;

            slow = slow->next;

        }

        return fast == slow;

    }

};