That solution is good for recursion. Ineffective. How would you implement that solution iteratively?

Can you describe more please. what is the purpose? is it tree serialization and deserialization?

the proposed solution will work for only binary tree. The question does not clarify about it. @Nir, what is a recursion you are referencing? You just traverse the tree in a way you like while keeping track to the "order number" of the element and place it to preallocated array.