Maximum of all subarrays of size k
Here you are using a few structures which I feel are not the right tool for the job.

Firstly, you are given an array of int, but you are returning a List&lt;Integer&gt;. I dislike List&lt;Integer&gt;, but even worse than using a List for primitives, is using a mixture of them. Be consistent!

The dueue is a confusing concept. It is worse because you use a for-loop in a non-traditional way, with the loop-variable declared outside the loop, and you reuse it later. You don't have any comments explaining how you use it.

At this point, I have looked through the requirements, I have figured out how I would do it. I can see that your strategy may have some advantages, if it does what I think it does, but it is complicated, and hard to read. So, I am giving up....

Code Review not successful, not commented enough, not enough background information.