chore(Python): add max sub array sum (#936)

algorithms/Python/README.md

@@ -7,6 +7,7 @@
 - [Missing Number](arrays/missing_number.py)
 - [Remove duplicate items](arrays/remove_duplicates_list.py)
 - [Dutch National Flag Algorithm](arrays/dutch_national_flag_algo.py)
+- [Max Sub Array Sum](arrays/max_sub_array_sum.py)
 
 ## Linked Lists
 - [Doubly](linked_lists/doubly.py)

algorithms/Python/arrays/max_sub_array_sum.py

@@ -0,0 +1,32 @@
+"""
+Algorithm Name: Max Sum of Sub Array
+Time Complexity: O(n)
+Explanation: arr = [3, 2, -4, 9]
+at the start of the algorithm
+assign current sum (max_sum_curr) = max sum(max_sum) = arr[0]
+(for) iterate from arr[1] to arr[n] and do
+  max_sum_curr = arr[i] if arr[i] > arr[i] + max_sum_curr
+  else 
+  max_sum_curr = max_sum_curr + arr[i]
+  max_sum = max_sum if max_sum > max_sum_curr
+  else 
+  max_sum = max_sum_curr
+end
+return max_sum
+"""
+
+def max_sub_arr_sum(arr): 
+    arr_size = len(arr)
+    max_sum = arr[0]
+    max_sum_curr = arr[0]
+     
+    for i in range(1, arr_size):
+        max_sum_curr = max(arr[i], max_sum_curr + arr[i])
+        max_sum = max(max_sum, max_sum_curr)
+         
+    return max_sum
+    
+
+# print("Enter array of numbers (Ex: 1 2 3 4 for [1, 2, 3, 4])")
+arr = [3, 2, -4, 9] # list(map(int, input().split()))
+print("Maximum Sub Array Sum is", max_sub_arr_sum(arr))