在比较时注意==和equals的使用
public boolean isPail (ListNode<Integer> head) { ArrayList<Integer> list = new ArrayList<>(); while (head != null) { list.add(head.val); head = head.next; } int size = list.size(); for (int i = 0; i < size/2; i++) { if (!list.get(i).equals(list.get(size - 1 - i))) { return false; } } return true; }