Leetcode 239 | Sliding Window Maximum (Linear time algorithm)

Sliding Window Maximum is a common interview question asked in google facebook amazon etc.

It is also present on leetcode as 239. Sliding Window Maximum

Given an array nums, there is a sliding window of size k which is moving from the very left of the array to the very right. You can only see the k numbers in the window. Each time the sliding window moves right by one position. Return the max sliding window.