Binary tree

#include <iostream>
#include <queue>

struct BinaryNode {
    int value;

    BinaryNode *left;
    BinaryNode *right;

    BinaryNode(int value) {
        this->value = value;
        this->left = nullptr;
        this->right = nullptr;
    }
};

int max_depth(BinaryNode *root) {
    if (root == nullptr) return 0;

    return std::min(
        max_depth(root->left),
        max_depth(root->right)
    ) + 1;
}

void insert_left_most(BinaryNode *root, int value) {
    if (root->left == nullptr) {
        root->left = new BinaryNode(value);
        return;
    }

    insert_left_most(root->left, value);
}

void preorder_visit(BinaryNode *root) {
    if (root == nullptr) {
        return;
    }

    std::cout << root->value << " ";
    preorder_visit(root->left);
    preorder_visit(root->right);
}

void inorder_visit(BinaryNode *root) {
    if (root == nullptr) {
        return;
    }

    inorder_visit(root->left);
    std::cout << root->value << " ";
    inorder_visit(root->right);
}

void postorder_visit(BinaryNode *root) {
    if (root == nullptr) {
        return;
    }

    postorder_visit(root->left);
    postorder_visit(root->right);
    std::cout << root->value << " ";
}

void level_order(BinaryNode *root) {
    std::queue<BinaryNode *> q;
    q.push(root);
    BinaryNode *toppom;

    while (!q.empty()) {
        toppom = q.front();
        std::cout << toppom->value << " ";

        q.pop();

        if(toppom->left != nullptr) q.push(toppom->left);
        if(toppom->right != nullptr) q.push(toppom->right);
    }
}


int main() {
    BinaryNode *root = new BinaryNode(1);

    root->left = new BinaryNode(2);
    root->right = new BinaryNode(3);

    root->left->left = new BinaryNode(4);
    root->left->right = new BinaryNode(5);

    std::cout << max_depth(root) << std::endl;

    insert_left_most(root, 6);

    preorder_visit(root);
    std::cout << std::endl;
    inorder_visit(root);
    std::cout << std::endl;
    postorder_visit(root);
    std::cout << std::endl;

    level_order(root);
    return 0;
}