Palindrome Linked List

1. Title

Palindrome Linked List

2. Http address

https://leetcode.com/problems/palindrome-linked-list/

3. The question

Given a singly linked list, determine if it is a palindrome.

Follow up:
Could you do it in O(n) time and O(1) space?

4. My code(AC)

        public ListNode getKthNode(ListNode head, int k)
    {
        
        int re = 1;
        ListNode p = head;
        while( re <= k && p != null)
        {
            if( re == k)
            {
                return p;
            }
            re++;
            p = p.next;
        }
        return null;
    }
    public int getLength(ListNode head)
    {
        int re = 0;
        ListNode p = head;
        while( p != null)
        {
            re++;
            p = p.next;
        }
        return re;
    }
    
        
    public ListNode revLinked(ListNode head)
    {
        ListNode dump = new ListNode(0);
        ListNode p = head;
        ListNode tmp = null;
        while( p != null)
        {
            tmp = p.next;
            p.next = dump.next;
            dump.next = p;
            p = tmp;
        }
        return dump.next;
    }
    
    
    public boolean isPalindrome(ListNode head) {
        
        if( head == null || head.next == null)
            return true;
        
        int len = getLength(head);
        ListNode p,q;
        q = getKthNode(head, (len / 2) + 1);
        q = revLinked(q);
        p = head;
        while( q != null && p != null)
        {
            if( q.val != p.val)
            {
                return false;
            }
            p = p.next;
            q = q.next;
        }
       return true;        
    }