how to use Binary tree search in Python

Question

# stack_depth is initialised to 0

def find_in_tree(node, find_condition, stack_depth):
    assert (stack_depth < max_stack_depth), 'Deeper than max depth'
    stack_depth += 1
    result = []
    if find_condition(node):
        result += [node]
    for child_node in node.children:
        result.extend(find_in_tree(child_node, find_condition, stack_depth))
    return result

I need help understanding this piece of code. The question i want to answer is

The Python function above searches the contents of a balanced binary tree. If an upper limit of 1,000,000 nodes is assumed what should the max_stack_depth constant be set to?

From what I understand, this is a trick question. If you think about it, stack_depth is incremented every time the find_in_tree() function is called in the recursion. And we are trying to find a particular node in the tree. And in our case we are accessing every single node every time even if we find the correct node. Because there is no return condition when stops the algorithm when the correct node is found. Hence, max_stack_depth should 1,000,000?

Can someone please try to explain me their thought process.

Answer 1

The key thing to notice is that stack_depth is passed down to each recursive call of the function. If it's a balanced binary tree then each call to find_in_tree will pass the same stack_depth value to up to two children. Just keep in mind that the reference to stack_depth is not shared between subsequent calls to find_in_tree. They will have their own version of stack_depth initialized to the value of the parent call.

This should be enough information to figure out what the value should be before the assert fires.