题解 | #NC96 判断一个链表是否为回文结构#

和力扣 234. 回文链表 相同

import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 * }
 */

public class Solution {
    /**
     * 
     * @param head ListNode类 the head
     * @return bool布尔型
     */
    public boolean isPail (ListNode head) {
        // write code here
        if (head == null || head.next == null) return true;
        ListNode A_end = mid(head);
        ListNode B_start = A_end.next;
        A_end.next = null;
        B_start = reverse(B_start);
        boolean res = compare(head, B_start);
        A_end.next = reverse(B_start);
        return res;
    }
    
    public ListNode mid(ListNode head) {
        ListNode f = head;
        ListNode s = head;
        while (f.next != null && f.next.next != null) {
            f = f.next.next;
            s = s.next;
        }
        return s;
    }
    
    public ListNode reverse(ListNode head) {
        ListNode pre = null;
        ListNode tmp = null;
        while (head != null) {
            tmp = head.next;
            head.next = pre;
            pre = head;
            head = tmp;
        }
        return pre;
    }
    
    public boolean compare(ListNode A, ListNode B) {
        while (B != null) {
            if (A.val != B.val) return false;
            A = A.next;
            B = B.next;
        }
        return true;
    }
}