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) {
        // write code here
        if (head == null) {
            return false;
        }
        if (head.next == null) {
            return true;
        }
        Stack<ListNode> st = new Stack<>();
        ListNode slow = head, fast = head;
        while (fast != null && fast.next != null) {
            st.add(slow);
            slow = slow.next;
            fast = fast.next.next;
        }
        if (fast == null) {
            while (!st.isEmpty()) {
                if (st.pop().val == slow.val) {
                    slow = slow.next;
                } else {
                    return false;
                }
            }
            return true;
        } else {
            slow = slow.next;
            while (!st.isEmpty()) {
                if (st.pop().val == slow.val) {
                    slow = slow.next;
                } else {
                    return false;
                }
            }
            return true;

        }

        // return false;
    }
}

整了个栈，将链表分为奇数个和偶数个节点进行运算，然后就比较简单了。