int height(Node* root) {
        struct Frame {
            Node* node{};
            int height = 0;
        };
        std::stack<Frame> stack;
        stack.push({root});
        int max = INT_MIN;
        while (!stack.empty()) {
            const auto top = stack.top();
            stack.pop();
            max = std::max(max, top.height);
            if (top.node->right)
                stack.push({top.node->right, top.height + 1});
            if (top.node->left)
                stack.push({top.node->left, top.height + 1});
        }
        return max;
    }