Fix Imports

Author: lighting9999

data_structures/binary_tree/diff_views_of_binary_tree.py

@@ -173,6 +173,7 @@ def binary_tree_bottom_side_view(root: TreeNode) -> list[int]:
     >>> binary_tree_bottom_side_view(None)
     []
     """
+    from collections import defaultdict
 
     def breadth_first_search(root: TreeNode, bottom_view: list[int]) -> None:
         """