Question

As mentioned in the Title , I have a Binary search tree. I want to convert it to sorted doubly linklist using recursion.

My code

 for each node in tree
   find max of left sub-tree and assign its right to present node ,present node left to max 
   find min of right sub-tree and assign its left to present node ,present node right to max 
   and now recursively do same thing to other nodes in BST .

but this solution is not efficient as it reaches each node more than one time .In my quest of optimized code i got a link from google greatTreeList sollution . I have searched the same in SO both sollutions are same and worked for me. I didnt understand the append function of the sollution as it contains code

join(alast,b)
join(blast,a)

For tree whose nodes are inserted in following order 10,5,9,6,8,7,12,11,13,14

can anyone please explain how
join(alast,b)
join(blast,a)

are linking node in each recursion call.

Answer 1

I think you are over thinking this actually quite easy task – extracting the data from a binary tree in order is as simple as doing a depth first traversal – this is the point of a binary tree that it very efficiently gives you the elements in the sorted order.

So what you need to do is a standard depth first walk of the tree and each time you find a node add it to you linked list.

This in order depth first recursion is fairly straight forward is pseudocode:

Traverse(Node N)
  Traverse(N.left);
  Add N to the linked list
  Traverse(N.right);

I suggest you try this manually on you example so you see how it works.