Leetcode 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.

For example,
Given nums = [1,3,-1,-3,5,3,6,7], and k = 3.

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

Therefore, return the max sliding window as [3,3,5,5,6,7].

Note: 
You may assume k is always valid, ie: 1 ≤ k ≤ input array's size for non-empty array.

Follow up:
Could you solve it in linear time?

 

public class Solution {
    public int[] MaxSlidingWindow(int[] nums, int k) {
        int len = nums.Length;
        if (len == 0 || len < k) return new int[0];
        
        var result = new int[len - k + 1];
        var window = new List<int>(k);
        
        for (int i = 0; i < len; i++)
        {
            while (window.Count > 0 && i - window[0] >= k)
            {
                window.RemoveAt(0);
            }
            
            while (window.Count >0 && nums[i] > nums[window[window.Count - 1]])
            {
                window.RemoveAt(window.Count - 1);
            }
            
            window.Add(i);
            
            if (i >= k - 1)
            {
                result[i - k + 1] = nums[window[0]];
            }
        }
        
        return result;
    }
}