题解 | #判断一个链表是否为回文结构#

import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 *   public ListNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param head ListNode类 the head
     * @return bool布尔型
     */
    public boolean isPail (ListNode head) {
        //快慢指针，确定中点
        ListNode fast = head.next,slow = head;
        while(fast !=null&&fast.next!=null){
            slow=slow.next;
            fast=fast.next.next;
        }
        //中点反转，遍历比较
        slow=Reverse(slow);
        ListNode q =head;
        while(q!=null){
            if(slow.val!=q.val)
            return false;
            slow=slow.next;
            q=q.next;
        }
        return true;
        
    }

//链表反转
    ListNode Reverse(ListNode head){
        ListNode prev = null;
        while(head !=null){
            ListNode next = head.next;
            head.next=prev;
            prev = head;
            head = next;
        }
        return prev;
    }
}