'lintcode 带环链表'

lintcode 带环链表

描述

给定一个链表，判断它是否有环。

样例

给出 -21->10->4->5, tail connects to node index 1，返回 true

挑战

不要使用额外空间

思路

快慢指针，如果有环，一定能在On时间内相遇。

代码

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/** * Definition of singly-linked-list: * class ListNode { * public: * int val; * ListNode *next; * ListNode(int val) { * this->val = val; * this->next = NULL; * } * } */ class Solution { public: /** * @param head: The first node of linked list. * @return: True if it has a cycle, or false */ bool hasCycle(ListNode * head) { // write your code here if (!head || !head->next) return false; ListNode *fast = head->next->next, *slow = head; while (fast && fast->next) { if (fast == slow && fast != NULL) return true; fast = fast->next->next; slow = slow->next; } return false; } };

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