### TechQ: Transfer Binary Tree From Machine A to Machine B

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TechQ: Transfer a binary tree from Machine A to Machine B. Binary tree can be any binary tree without any constraints.
Algorithm: The standard algorithm is sending the inorder and pre-order from machine A to machine B and reconstructing the tree on machine B. We know its not possible to reconstruct a tree using just a preorder traversal alone as it does not track the depth here we present the algorithm where we reconstruct the tree on machine B, using just the pre-order traversal using some additional flags which are in a way used to keep track of the depths.
Machine A sends the nodes to machine B in preorder, with one additional thing wherein we also send a null whenever the node doesn’t have either left or right child.
For example, for tree shown in the image the sequence generated will be: 2,7,2,NULL,NULL,6,5,NULL,NULL,11,NULL,NULL,5,NULL,9,4,NULL,NULL,NULL, DONE. This is modified pre-order traversal where we also send NULL whenever right or left child of node is NULL.

The pseudocode on Machine A will be like:
`PUSH(node *root){If(root== NULL){ Send(NULL); Return;}Else{ Send(root->VAL);PUSH(root->left);PUSH(root->right);}}`
When we want to send a binary tree from machine A we will just call:
`PUSH(root);SEND(“DONE”);`

On machine B we need to reconstruct the tree based on this sequence, before going ahead I would like to show that the sequence generated will be unique for any given tree.

1

/ \

2 3

Seq: 1,2,N,N,3,N,N,D

1

/

2

/

3

Seq: 1,2,3,N,N,N,N,D

1

/

2

\

3

Seq: 1,2,N,3,N,N,N,D

As you can see from above example its clear that no two different trees can generate the same sequence. Now we will write a pseudocode on Machine B which will PULL the nodes from machine A.

`PULL(node *root){ Node * tmp=new node(); tmp->VAL= GetFromA(); if(tmp->VAL==”DONE”) return; if(tmp->VAL==”NULL”) tmp=NULL; root=tmp; if(root!=NULL) { PULL(root->left); PULL(root->right); }}`

On Machine B when we want to pull binary tree we need to just call

`Node *root=null;PULL(root);`

If you guys find any flaw in above approach, feel free to post it as comments below.