dfs/on_tree/max_depth_binary_tree

class Node:
	def __init__(self, val, left = None, right = None):
		self.val = val;
		self.left = left;
		self.right = right;

def tree_max_depth(root):
	def dfs(root):
		if root is None:
			return 0
		return max(dfs(root.left), dfs(root.right)) + 1
	return dfs(root) - 1 if root else 0;

def build_tree(nodes, f):
    val = next(nodes)
    if val == "x":
        return None
    left = build_tree(nodes, f)
    right = build_tree(nodes, f)
    return Node(f(val), left, right)

if __name__ == "__main__":
    root = build_tree(iter(input().split()), int)
    res = tree_max_depth(root)
    print(res)

#include <algorithm>
#include <iostream>
#include <iterator>
#include <sstream>
#include <string>
#include <vector>

template<typename T>
struct Node {
    T val;
    Node<T>* left;
    Node<T>* right;

    explicit Node(T val, Node<T>* left = nullptr, Node<T>* right = nullptr)
        : val{val}, left{left}, right{right} {}

    ~Node() {
        delete left;
        delete right;
    }
};

int dfs(Node<int>* root) {
	if (root == nullptr) {
		return 0;
	}
	return std::max(dfs(root->left), dfs(root->right)) + 1;
}

int tree_max_depth(Node<int>* root) {
	return root ? dfs(root) - 1 : 0;
}

// this function builds a tree from input
// learn more about how trees are encoded in https://algo.monster/problems/serializing_tree
template<typename T, typename Iter, typename F>
Node<T>* build_tree(Iter& it, F f) {
    std::string val = *it;
    ++it;
    if (val == "x") return nullptr;
    Node<T>* left = build_tree<T>(it, f);
    Node<T>* right = build_tree<T>(it, f);
    return new Node<T>{f(val), left, right};
}

template<typename T>
std::vector<T> get_words() {
    std::string line;
    std::getline(std::cin, line);
    std::istringstream ss{line};
    ss >> std::boolalpha;
    std::vector<T> v;
    std::copy(std::istream_iterator<T>{ss}, std::istream_iterator<T>{}, std::back_inserter(v));
    return v;
}

int main() {
    std::vector<std::string> root_vec = get_words<std::string>();
    auto root_it = root_vec.begin();
    Node<int>* root = build_tree<int>(root_it, [](auto s) { return std::stoi(s); });
    int res = tree_max_depth(root);
    std::cout << res << '\n';
}

"use strict";

class Node {
    constructor(val, left = null, right = null) {
        this.val = val;
        this.left = left;
        this.right = right;
    }
}

function dfs(root) {
    if (root === null) {
        return 0;
    }
    return Math.max(dfs(root.left), dfs(root.right)) + 1;
}

function treeMaxDepth(root) {
    // WRITE YOUR BRILLIANT CODE HERE
    return root !== null ? dfs(root) - 1 : 0;
}

// this function builds a tree from input; you don't have to modify it
// learn more about how trees are encoded in https://algo.monster/problems/serializing_tree
function buildTree(nodes, f) {
    const val = nodes.next().value;
    if (val === "x") return null;
    const left = buildTree(nodes, f);
    const right = buildTree(nodes, f);
    return new Node(f(val), left, right);
}

function splitWords(s) {
    return s === "" ? [] : s.split(" ");
}

function* main() {
    const root = buildTree(splitWords(yield)[Symbol.iterator](), parseInt);
    const res = treeMaxDepth(root);
    console.log(res);
}

class EOFError extends Error { }

{
    const gen = main();
    const next = (line) => gen.next(line).done && process.exit();
    let buf = "";
    next();
    process.stdin.setEncoding("utf8");
    process.stdin.on("data", (data) => {
        const lines = (buf + data).split("\n");
        buf = lines.pop();
        lines.forEach(next);
    });
    process.stdin.on("end", () => {
        buf && next(buf);
        gen.throw(new EOFError());
    });
}