You need enough knowledge about inorder, postorder and preorder tree traverse to solve this problem. A preorder, postorder  and inorder tree traverse result can be shown recursively as follows:

Preorder :   root  left subtree  right sutree

Inorder   :   left subtree  root  right sutree

Postorder : left subtree  right sutree   root

Now just do the same thing recursively.

Oh�. You have to write a recursive program.