Solution.java

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public boolean isPalindrome(ListNode head) {
        if (head==null||head.next==null) {
            return true;
        }
        ListNode slow=head;
        ListNode fast=head;
        while (fast!=null&&fast.next!=null) {
            slow=slow.next;
            fast=fast.next.next;
        }
        ListNode test=f(slow);
        while (test!=null) {
            if (test.val!=head.val) {
                return false;
            }
            test=test.next;
            head=head.next;
        }
        
        return true;
    }
    //原地翻转链表
    public ListNode f(ListNode node){
        if (node==null||node.next==null) {
            return node;
        }
        ListNode l=node.next;
        ListNode h;
        node.next=null;
        while (l!=null) {
            h=l.next;
            l.next=node;
            node=l;
            l=h;
        }
        return node;
    }
}