CC2.7.java

    public boolean isPalindrome(ListNode head) {
        if(head == null)
            return true;
        Stack<Integer> S = new Stack<Integer>();
        ListNode cur = head;
        while(cur != null) {
            S.push(cur.val);
            cur = cur.next;
        }
        cur = head;
        while(cur != null) {
            if(S.pop() != cur.val)
                return false;
        }
        return true;
    }