Сегодня я узнал: Инвертировать бинарное дерево

tree =      1
          /   \
        2       3
      /   \   /   \
     4    5  6     7
   /   \
  8     9

tree =      1
          /   \
        3       2
      /   \   /   \
     7    6  5     4
                 /   \
                9     8

def invert_binary_tree(tree):
    queue = [tree]
    while len(queue) > 0:
        cur_node = queue.pop(0)
        if cur_node is not None: 
            cur_node.left, cur_node.right = cur_node.right, cur_node.left
            queue.append(cur_node.left)
            queue.append(cur_node.right)
    return tree


# This is the class of the input binary tree.
class BinaryTree:
    def __init__(self, value):
        self.value = value
        self.left = None
        self.right = None