# Time: O(N)
# Space: O(1)
class Solution:
    def findMaxAverage(self, nums: List[int], k: int) -> float:
        # Sliding window approach
        max_average = float("-inf")
        moving_sum = 0.0
        window_start = 0
        
        for i in range(0, len(nums)):
            moving_sum += nums[i]
            
            # Need to start computing averages only at this point.
            # e.g. Suppose nums = [0, 1, 2, 3] and k = 3
            if i >= k - 1:
                # e.g. When i = 3 - 1 = 2, start checking for max average
                max_average = max(moving_sum / k, max_average)
                
                # e.g. Remove element at beginning of window, i.e 0 from [0...2]
                moving_sum -= nums[window_start]
                
                # e.g. Move window position from 0 to 1
                window_start += 1
        
        return max_average