239\. Sliding Window Maximum

Hard

You are given an array of integers `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_.

**Example 1:**

**Input:** nums = [1,3,-1,-3,5,3,6,7], k = 3

**Output:** [3,3,5,5,6,7]

**Explanation:**

    Window position        Max
    ---------------       -----
    [1 3 -1] -3 5 3 6 7     3
    1 [3 -1 -3] 5 3 6 7     3
    1 3 [-1 -3 5] 3 6 7     5
    1 3 -1 [-3 5 3] 6 7     5
    1 3 -1 -3 [5 3 6] 7     6
    1 3 -1 -3 5 [3 6 7]     7 

**Example 2:**

**Input:** nums = [1], k = 1

**Output:** [1] 

**Example 3:**

**Input:** nums = [1,-1], k = 1

**Output:** [1,-1] 

**Example 4:**

**Input:** nums = [9,11], k = 2

**Output:** [11] 

**Example 5:**

**Input:** nums = [4,-2], k = 2

**Output:** [4] 

**Constraints:**

*   <code>1 <= nums.length <= 10<sup>5</sup></code>
*   <code>-10<sup>4</sup> <= nums[i] <= 10<sup>4</sup></code>
*   `1 <= k <= nums.length`