C++ "Cây nhị phân"

#include <iostream>
#include <math.h>
using namespace std;

typedef struct node {
    int data;
    struct node *left;
    struct node *right;
} node;

node* createNode(int _data = 0, node* left = NULL,
                 node* right = NULL){
    node* temp = new node;
    temp->data = _data;
    temp->left = left;
    temp->right = right;
    return temp;
}



node* createTree(){
    node *left, *right, *right2;
    left = createNode(3);
    right = createNode(7);
    left = createNode(10, left, right);
    right = createNode(20);
    right = createNode(30, left, right);
    left = createNode(5);
    right2 = createNode(15);
    left = createNode(20, left, right2);
    node* root = createNode(50, left, right);
    return root;
}

void destroyTree(node* root){
    if (!root) return;
    destroyTree(root->left);
    destroyTree(root->right);
    cout << root->data << endl;
    delete root;
}

int check(int num){
    for(int i = 2; i <= sqrt(num); i++)
        if (num % i == 0) return 0;
    return 1;
}

void preorder(node* root){
    if (root){
        preorder(root->left);
        int num = root -> data;
        if(check(num) == 1){
            cout << num << " ";
        }
        preorder(root->right);
    }
}

int height(node* root){
    if (!root) return -1;
    else return 1 + max(height(root->left),
                        height(root->right));
}

int leafCount(node* root){
    if (!root->left && !root->right) return 1;
    else return leafCount(root->left) + leafCount(root->right);
}

int main(){
    node* root = createTree();
    cout << height(root) << endl;
    cout << leafCount(root) << endl;
    preorder(createTree());
    destroyTree(root);
    return 0;
}