Palindrome Linked List

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

Recursive

public class Solution {

    private ListNode head;

    private boolean helper(ListNode tail) {
        if(tail == null) return true;

        if(helper(tail.next) && head.val == tail.val){
            head = head.next;
            return true;
        }else return false;
    }

    public boolean isPalindrome(ListNode tail){
        head = tail;
        return helper(tail);
    }
}