AlyonaTrees

#include <iostream>

using namespace std;

struct TreeNode {
    int data;
    TreeNode *left;
    TreeNode *right;
};

TreeNode *root;

void buildTree(); // Функция постройки дерева
void insertFromChild(TreeNode*, int);
void insertFromRoot(int);
void destroyTree(TreeNode*);
void preorderPrint(TreeNode*);
void findMaxValue(TreeNode*, int&);

int main() {
    setlocale(LC_ALL, "rus");
    buildTree();
    preorderPrint(root);
    int k = -1e9 - 1;
    if (root != NULL) {
        k = root->data;
        findMaxValue(root, k);
        cout << "\nНаибольшое значение ключа из всех узлов дерева: " << k << '\n';
    } else
        cout << "\nВаше дерево пустое!\n";
    destroyTree(root);
    return 0;
}

void insertFromChild(TreeNode *leaf, int key) {
    if (key < leaf->data) {
        if (leaf->left != NULL)
            insertFromChild(leaf->left, key);
        else {
            leaf->left = new TreeNode;
            leaf->left->data = key;
            leaf->left->left = NULL;
            leaf->left->right = NULL;
        }
    }
    else {
        if (leaf->right != NULL)
            insertFromChild(leaf->right, key);
        else {
            leaf->right = new TreeNode;
            leaf->right->data = key;
            leaf->right->left = NULL;
            leaf->right->right = NULL;
        }
    }
}

void insertFromRoot(int key) {
    if (root != NULL) {
        insertFromChild(root, key);
    }
    else {
        root = new TreeNode;
        root->data = key;
        root->left = NULL;
        root->right = NULL;
    }
}

void buildTree() {
    int n;
    cout << "Enter count of elements to insert in bintree:\n";
    cin >> n;
    cout << "Input elements:\n";
    for (int i = 0; i < n; i++) {
        int req;
        cin >> req;
        insertFromRoot(req);
    }
}

void destroyTree(TreeNode *leaf) {
    if (leaf != NULL) {
        destroyTree(leaf->left);
        destroyTree(leaf->right);
        delete leaf;
    }
}

void preorderPrint(TreeNode *root) {
    if (root == NULL) {
        return;
    }
    cout << root->data << ' ';
    preorderPrint(root->left);
    preorderPrint(root->right);
}

void findMaxValue(TreeNode *root, int &maxValue) {
    if (root == NULL) {
        return;
    }
    maxValue = max(maxValue, root->data);
    findMaxValue(root->left, maxValue);
    findMaxValue(root->right, maxValue);
}