【剑指offer】滑动窗口的最大值

public ArrayList<Integer> (int[] num, int size) {
    ArrayList<Integer> result = new ArrayList<>();

    if (num == null || num.length < 1 || size < 1)
        return result;

    LinkedList<Integer> deque = new LinkedList<>();

    for (int i = 0; i < num.length; i++) {
        while (!deque.isEmpty() && num[i] > num[deque.peekLast()])
            deque.pollLast();

        deque.offerLast(i);

        if (i - deque.peekFirst() > size - 1)
            deque.pollFirst();

        if (i >= size - 1)
            result.add(num[deque.peekFirst()]);
    }

    return result;
}