Java [Leetcode 234]Palindrome Linked List
题目描述:
Given a singly linked list, determine if it is a palindrome.
Follow up:
Could you do it in O(n) time and O(1) space?
解题思路:
使用O(n)的时间复杂度及O(1)的时间复杂度表明顺序遍历链表以及不能够开辟跟链表相当的空间,这样可以找出中间的位置,然后将后半部分的链表反转,然后跟前半部分的链表逐个位置比对。
代码如下:
/** * Definition for singly-linked list. * public class ListNode { * int val; * ListNode next; * ListNode(int x) { val = x; } * } */ public class Solution { public boolean isPalindrome(ListNode head) { ListNode end = head; ListNode mid = head; while(end != null && end.next != null){ end = end.next.next; mid = mid.next; } if(end != null) //in case of odd list mid = mid.next; mid = reverseList(mid); while(mid != null){ if(mid.val != head.val) return false; mid = mid.next; head = head.next; } return true; } public ListNode reverseList(ListNode head){ ListNode pre = null, next = null; while(head != null){ next = head.next; head.next = pre; pre = head; head = next; } return pre; } }