题解 | #判断一个链表是否为回文结构#

思路，链表反转后逐一比较

注意的是：链表不能直接反转，否则结构发生变化，需要新复制一个链表进行操作

import java.util.*;
public class Solution {
    //反转链表指针
    ListNode reverse(ListNode head) { //反转链表，链表结构会发生变化
        //前序节点
        ListNode prev = null;
        while(head != null){
            //断开后序
            ListNode next = head.next; 
            //指向前序
            head.next = prev; 
            prev = head;
            head = next;
        }
        return prev;
    }
    
     public boolean isPail(ListNode head) {
        ListNode dummyHead = new ListNode(-1);//定义一个新链表
        //copy orgin list to p1
        ListNode p1 = dummyHead;
        ListNode p2 = head;
        while (p2 != null) {//将链表复制给新链表,不能动原链表
            p1.next = new ListNode(p2.val);
            p2 = p2.next;
            p1 = p1.next;
        }
        //traverse the orgin list and reversed list
        p1 = dummyHead.next;
        p2 = reverse(head);
        while (p1 != null ) {
            if (p1.val != p2.val) {
                return false;
            }
            p1 = p1.next;
            p2 = p2.next;
        }
        return true;
    }
}