struct odp{
    int height;
     bool ok;
};

odp ifBST(BSTnode * root){
    odp o;
    o.ok=true;
    if(root == NULL){
        o.height=0;
    }
    else{
        odp leftHeight = ifBST(root->left) , rightHeight = ifBST(root->right);
        if(abs(leftHeight.height-rightHeight.height)>1){
            o.ok=false;
        }
        o.height = 1 + max(leftHeight.height, rightHeight.height);
    }
    return o;
}