add py3 soln max subarray

0643_maximum-average-subarray-i/python3/solution.py

@@ -0,0 +1,25 @@
+# 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