题解 | #判断一个链表是否为回文结构#

/*
 * 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
        ListNode fast = head;
        ListNode slow = head;
        while(fast.next != null && fast.next.next != null){
            fast = fast.next.next;
            slow = slow.next;
       }
        ListNode l = reserve(slow.next);
        slow = head;
        while(slow != null && l != null){
            if(slow.val != l.val){
                return false;
            }
            slow = slow.next;
            l = l.next;
        }
        return true;
    }
    public ListNode reserve(ListNode head){
        ListNode pre = null;
        ListNode cur = head;
        while(cur != null){
            ListNode node = cur.next;
            cur.next = pre;
            pre = cur;
            cur = node;
        }
        return pre;
    }
}