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 class Solution {
    /**
     * 翻转后半部分链表
     * @param head ListNode类 the head
     * @return bool布尔型
     */
    public boolean isPail (ListNode head) {
        if (head == null) return false;
        // write code here
        ListNode slow = head, fast = head, pre = head;
        while (fast != null) {
            pre = slow;
            slow = slow.next;
            fast = fast.next;
            if (fast != null) fast = fast.next;
        }
        pre.next = null;
        ListNode reverse = reverse(slow);
        ListNode T = head;
        while (T != null && reverse != null) {
            if (T.val != reverse.val) return false;
            T = T.next;
            reverse = reverse.next;
        }
        return true;
    }

    public ListNode reverse(ListNode node) {
        ListNode pre = null;
        ListNode cur = node;
        while (cur != null) {
            ListNode T = cur.next;
            cur.next = pre;
            pre = cur;
            cur = T;
        }
        return pre;
    }
}