int tree :: f(tree_node *root, int k)
{
    if(!root)
        return 0;
    return count_on_lvl_less_k(root,k)+f(root->left,k)+f(root->right,k);
}
void tree :: f4(tree_node *root, int *a, int level)
{
    if(!root)
        return;
    a[level]++;
    f4(root->left, a,level+1);
    f4(root->right, a,level+1);
}
int tree :: count_on_lvl_less_k(tree_node *root, int k)
{
    int *a;
    int lvl=0, count_lvl = depth(root);
    if(!root)
        return 0;
    a = new int [count_lvl+1];
    for(lvl=0; lvl<count_lvl; lvl++)
        a[lvl] = 0;
    f4(root,a,0);
    for(lvl=0; lvl<count_lvl; lvl++)
    {
        if(a[lvl] > k)
        {
            delete a;
            return 0;
        }
    }
    delete a;
    return 1;
}