Interview task on binary trees - oop

Question

Task: transfer a server side binary tree to client.
I got this task in an interview. Is there any efficient way to do this?
I don't understand the task very well myself.
This is what I came up with, but not sure about server to client trasfer. Any ideas?
void copyInOrder(TNode *orgTree, Tnode *& copyTree)
{
if(orgTree !=NULL){
//left side
TNode newLeftNode = cloneNode(orgTree->left_link);
copyTree->left_link = newLeftNode;
copyInOrder(orgTree->left_link, copyTree->left_link);
//right side
TNode newRightNode = cloneNode(orgTree->right_link);
copyTree->right_link = newRightNode;
copyInOrder(orgTree->right_link, copyTree->right_link);
}
}

Answer 1

Honestly, defining "efficient" would be a good first step. What is considered important? Network bandwidth? Server side computation involved? Client side computation involved?
Along the same lines, what is the data?
For example, if the data is integers and network bandwidth is important, you could do construct an array of ints from the tree, transfer that with minimal overhead, and then convert it back to a binary tree on the user's end.
If server side load is the most important thing, you'd go a different route. If client side load, possibly yet another.
Its worth noting that, since this is an interview question, discussing with the interviewer what they find important for efficiency and how it affects the solution may be just as important as the actual solution you come up with.

Answer 2

To me, the problem seems to be not so much about the transfer itself, but how one would package the data to be transferred. The important thing to note is that since you are transferring bytes, as opposed to C++ objects, you will not be able to preserve the structure of the tree so easily during the transfer.
Therefore, I would suggest that you serialize the tree, and then send it over the network. You would obviously need to a pre-determined serialization scheme that the client knows about, so that the client can recreate the tree from the bytes it receives.

Answer 3

It suffices to show how to convert a given binary tree T to a sequence S of values in such a way that we can reconstruct T from S at the client side. One possible way is to use the well know fact:
We can construct a binary tree uniquely from its inorder and preorder
traversals.
Thus we can let S be the inorder traversal followed by the preorder traversal. Check the answer of this question.