LeetCode刷题笔记（链表）：linked-list-cycle

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• 转载请注明作者和出处：http://blog.csdn.net/u011475210
• 代码地址：https://github.com/WordZzzz/Note/tree/master/LeetCode
• 刷题平台：https://www.nowcoder.com/ta/leetcode
• 题  库：Leetcode经典编程题
• 编  者：WordZzzz

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题目描述

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

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

解题思路

又双叒叕是快慢指针，话不多说，上代码。

C++版代码实现

/**
 * 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 == NULL || head->next == NULL)
            return false;
        ListNode *fast = head;
        ListNode *slow = head;
        while(fast->next != NULL && fast->next->next != NULL){
            slow = slow->next;
            fast = fast->next->next;
            if(slow->val == fast->val)
                return true;
        }
        return false;
    }
};

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