239-Sliding Window Maximum

Title: Returns the maximum sliding window

def maxSlidingWindow(nums,k):
    if not nums:
        return []
    window,res = [],[]
    for i ,x in enumerate(nums):
        if i>=k and window[0]<=i-k:
            window.pop(0)
        while window and nums[window[-1]] <= x:
            window.pop()
        window.append(i)
        if i >= k-1:
            res.append(nums[window[0]])
    return res