题目描述:
判断有序list是不是环
要求:
时间复杂度o(n)
原文描述:
Given a linked list, determine if it has a cycle in it.
Follow up:
Can you solve it without using extra space?
思路:
- 设置两个指针,一个快指针,每次走两步,一个慢指针,每次走一步
- 如果块指针==慢指针,那么包含环
- 注意判断空值和长度为一的情况 -
代码:
/** * Definition for singly-linked list. * class ListNode { * int val; * ListNode next; * ListNode(int x) { * val = x; * next = null; * } * } */public class Solution { public boolean 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) { fast = fast.next.next; slow = slow.next; if(slow == fast) { return true; } } return false; }}