modified fenwich tree file

Author: arvinder004

pydatastructs/trees/fenwich_tree.py

@@ -86,4 +86,5 @@ def range_sum(self, start_index, end_index):
         if start_index == 0:
             return self.prefix_sum(end_index)
         else:
-            return self.prefix_sum(end_index) - self.prefix_sum(start_index - 1)
+            return self.prefix_sum(end_index) - self.prefix_sum(start_index - 1)
+