题解 | #牛群编号的回文顺序#

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 
     * @return bool布尔型
     */
    public boolean isPalindrome (ListNode head) {
        // write code here
        if (head == null || head.next == null) return true;
        // 找中点
        ListNode slow = head, fast = head;
        while (fast.next != null && fast.next.next != null) {
            slow = slow.next;
            fast = fast.next.next;
        }
        // 中点之后的节点入栈
        Stack<ListNode> stack = new Stack<>();
        while (slow.next != null) {
            stack.push(slow.next);
            slow = slow.next;
        }
        ListNode cur = head;
        // 依次弹出栈中元素比较
        while (!stack.isEmpty()) {
            if (cur.val != stack.pop().val) return false;
            cur = cur.next;
        }
        return true;
    }
}