Leetcode 234:palindrome Linked List

Given a singly linked list, determine if it is a palindrome.

Follow up:
Could do it in O (n) time and O (1) space?

Ideas

The first is divided into two parts of the same size (possibly 1), reverse a list. and then compare.

[CODE]

/** * Definition for singly-linked list. * public class ListNode {* int val; * ListNode Next; * ListNode (int x) {val = x;}} * *//1 2 3 2 1;        1 2 3 3 2 1;public class Solution {public boolean ispalindrome (ListNode head) {//input check ABCBA ABCCBA                if (Head==null | | head.next==null) return true;        ListNode middle = partition (head);                Middle = reverse (middle);            while (Head!=null && middle!=null) {if (head.val! = Middle.val) return false;            head = Head.next;        middle = middle.next;    } return true;        } private ListNode partition (ListNode head) {ListNode p = head;            while (P.next!=null && p.next.next!=null) {p = p.next.next;        head = Head.next;        } p = Head.next;        Head.next = null;    return p;     } Private ListNode reverse (ListNode head) {if (Head==null | | head.next==null) return head;   ListNode pre = head;        ListNode cur = head.next;        Pre.next = null;                ListNode NXT = null;            while (cur!=null) {nxt = Cur.next;            Cur.next = pre;            Pre = cur;        cur = NXT;    } return pre; }}

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Leetcode 234:palindrome Linked List