Improved del_node func

There was some logical error in implementation of delete node function.

Also we don't need to find balance factor 2 times so made separate variable.

Author: ShauryaDusht

data_structures/binary_tree/avl_tree.py

@@ -196,8 +196,13 @@ def get_left_most(root: MyNode) -> Any:
 
 
 def del_node(root: MyNode, data: Any) -> MyNode | None:
+    if root is None:
+        print("Nothing to delete")
+        return None
+        
     left_child = root.get_left()
     right_child = root.get_right()
+    
     if root.get_data() == data:
         if left_child is not None and right_child is not None:
             temp_data = get_left_most(right_child)
@@ -221,20 +226,23 @@ def del_node(root: MyNode, data: Any) -> MyNode | None:
     else:
         root.set_right(del_node(right_child, data))
 
-    if get_height(right_child) - get_height(left_child) == 2:
+    root.set_height(my_max(get_height(root.get_right()), get_height(root.get_left())) + 1)
+    
+    balance_factor = get_height(root.get_left()) - get_height(root.get_right())
+    
+    if balance_factor == 2:
         assert right_child is not None
         if get_height(right_child.get_right()) > get_height(right_child.get_left()):
             root = left_rotation(root)
         else:
             root = rl_rotation(root)
-    elif get_height(right_child) - get_height(left_child) == -2:
+    elif balance_factor == -2:
         assert left_child is not None
         if get_height(left_child.get_left()) > get_height(left_child.get_right()):
             root = right_rotation(root)
         else:
             root = lr_rotation(root)
-    height = my_max(get_height(root.get_right()), get_height(root.get_left())) + 1
-    root.set_height(height)
+            
     return root