题解 | #判断一个链表是否为回文结构#

using System;
using System.Collections.Generic;

/*
public class ListNode
{
	public int val;
	public ListNode next;

	public ListNode (int x)
	{
		val = x;
	}
}
*/

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 bool isPail (ListNode head) {
        if(head == null || head.next == null) return true;
        ListNode slow = head;
        ListNode fast = head;
        ListNode nex = null;
        ListNode pre = null;
        while(fast != null && fast.next != null){
            fast = fast.next.next;

            nex = slow.next;
            slow.next = pre;
            pre = slow;
            slow = nex;
        }
        bool isPalindrome = true;
        ListNode l1 = pre;
        ListNode l2 = slow;
        if(fast != null) l2 = l2.next;
        while(l1 != null){
            if(l1.val != l2.val) isPalindrome = false;
            pre = l1.next;
            l1.next = nex;
            nex = l1;
            l1 = pre;
            l2 = l2.next;
        }
        return isPalindrome;
    }
}