题解 | #判断一个链表是否为回文结构#

import java.util.*;
public class Solution {
    //反转链表指针 fast-template
    ListNode reverse(ListNode head) {
        //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) {
        //空链表直接为回文
        if(head == null)
            return true;
        //准备快慢双指针
        ListNode slow = head;
        ListNode fast = head;
        //双指针找中点
        while(fast != null && fast.next != null){
            slow = slow.next;
            fast = fast.next.next;
        }
        //中点处反转
        slow = reverse(slow);
        fast = head;
        while (slow != null) {
            //比较判断节点值是否相等
            if (slow.val != fast.val)
                return false;
            fast = fast.next;
            slow = slow.next;
        }
        return true;
    }
}