234. Palindrome Linked List

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

题目含义：给定一个单列表，判断是否构成回文

    public boolean isPalindrome(ListNode head) {
        Stack<Integer> valueStack = new Stack<>();
        if (head == null) return true;
        ListNode runer = head;
        ListNode walker = head;
        while (runer.next != null && runer.next.next != null)
        {
            valueStack.push(walker.val);
            runer = runer.next.next;
            walker = walker.next;
        }
        if (runer.next != null)
        {
//            列表有偶数个节点
            if (walker.val != walker.next.val) return false;
            walker = walker.next.next;
        }else{
            walker = walker.next;
        }
        while (walker != null)
        {
            if (walker.val != valueStack.pop()) return false;
            walker = walker.next;
        }
        return true;
        
    }