We consider a variant of BST where $\texttt{left(n)}$  $\leq$  $n$ $<$ $\texttt{right(n)}$ and this for any node $\texttt{n}$ in the tree.

Write a function that calculates the number of distinct values in this kind of binary tree. Give the corresponding declaration.

int nb_distinct(BST B)
{
    if(B)
    {
        if(B->left && B->data==B->left->data)
            return nb_distinct(B->left) + nb_distinct(B->right);
        return 1+ nb_distinct(B->left) + nb_distinct(B->right);
    }
    return 0;
}