Leetcode 线性表 Linked List Cycle

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Linked List Cycle

 Total Accepted: 17041 Total Submissions: 48975

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

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

题意：判断一个链表中是否有环

思路：快慢指针，如果有环，最终快慢指针会在非NULL相遇

注：用到fast->next前先要确保fast非NULL,要用fast->next->next前先要确保fast,fast->next非NULL

复杂度：时间O(n)， 空间O(1)

相关题目：Linked List CycleII

/** * 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 *fast, *slow;    fast = slow = head;    while(fast && fast->next){    fast = fast->next->next;    slow = slow->next;    if(fast == slow) return true;    }    return false;    }