原题:
Given a linked list, determine if it has a cycle in it.
=>给定一个单向链表,如何判断它里面是否有环存在。
Follow up:
Can you solve it without using extra space?
=>能否不使用额外的空间来解决这个问题?
/** * 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) { // IMPORTANT: Please reset any member data you declared, as // the same Solution instance will be reused for each test case. } };
晓东分析:
这是一个经典的题目了,他的解题思路就是使用快慢指针,就像我们以前学过的初中(or小学)数学题,只要两者的速度不同,在一个环内,终归是会追上的。当然我们一般的题目都是多长时间追上啊之类的问题。很简单吧,直接看代码了。
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) { // IMPORTANT: Please reset any member data you declared, as // the same Solution instance will be reused for each test case. ListNode *slow = head; ListNode *fast = head; while(fast != NULL && fast->next != NULL){ slow = slow->next; fast = fast->next->next; if(fast == slow) return true; } return false; } };
执行结果:
16 / 16test cases passed.
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Status:
Accepted |
Runtime: 76 ms
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希望大家有更好的算法能够提出来,不甚感谢。
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