First of all, we need to mention a software called Homebrew

Homebrew is probably the best package manager on Mac. It is equivalent to Ubuntu apt and command-line app store

Homebrew
brew

Max Howell is the author of Homebrew. When he went to google for an interview, the interviewer gave a question about reversing the binary tree. However, Max Howell didn't answer it. Finally, he became a good story

Invert binary tree

• Google Interviewer: when Max Howell, the star programmer, comes to our big Google, he must stay! He can't give too difficult questions or be too straightforward; so the questions should be simple and forced, and the tree structure should be more appropriate. The most common tree is the binary tree, and the most tested one is the binary search tree, so reverse the binary tree, ha ha, I'm really considerate!

• Max Howell: nature makes people

class Node(object):
    def __init__(self, value = None):
        self.value = value
        self.left = None
        self.right = None



class Tree(object):
    def __init__(self):
        self.root = Node()
        self.queue = []
        pass

    def add(self, value):
        # Create a node
        tmp_node = Node(value)
        # If the root node is empty, add the root node
        if len(self.queue) == 0:
            self.root = tmp_node
            self.queue.append(tmp_node)
        # If the root node is not empty
        else:
            # Get the node whose current subtree is not full (current temporary parent node)
            nowRoot = self.queue[0]
            # If the left subtree of the temporary parent node is empty
            if nowRoot.left == None:
                nowRoot.left = tmp_node
                self.queue.append(tmp_node)
            # If the right subtree of the temporary parent node is empty
            else:
                nowRoot.right = tmp_node
                self.queue.append(tmp_node)
                # Clear parent from queue (this parent is now full)
                self.queue.pop(0)
    # Sequential traversal
    def recursion_lvr(self, root):
        # If the node is empty, return
        if not root:
            return
        self.recursion_lvr(root.left)
        print(root.value)
        self.recursion_lvr(root.right)

    # Invert binary tree
    def reverse_tree(self, root):
        if not root:
            return
        # Get the root node of the current left and right subtrees
        tmp_left_node = root.left
        tmp_right_node = root.right

        # Reverse left and right subtrees of binary trees
        root.left = tmp_right_node
        root.right = tmp_left_node

        # Add left and right subtrees to the new sequence
        self.reverse_tree(root.left)
        self.reverse_tree(root.right)



def main():
    tree = Tree()
    for i in range(1,8):
        tree.add(i)

    tree.recursion_lvr(tree.root);

    tree.reverse_tree(tree.root)


    print("Results after reversal:")
    tree.recursion_lvr(tree.root);


if __name__ == '__main__':
    main()