Scheme中的树排序功能

Question

Im struggling with this problem for over 2 days now and still somehow I cannot solve it. I have to write a function in SCHEME that takes a list in a tree and displays items in sorted order.

The way I define trees is '(6 (left... ) (right...))

My function to choose a tree:

(define (tree-sort tree)
 (cond  ((null? tree) '())
    ((> (car tree) (cadr tree))
     (tree-sort (cadr tree)))
    (else
     (tree-sort (caddr tree))))
)

So I guess I should also have a function that sorts the most indepth list? I really dont get it and this is the last time I will ever have to deal with scheme. I have never used stackoverflow so please excuse me if the formating is wrong.

Kindly thank you!

Answer 1

Now that you clarified that the tree is already sorted, then you're looking for an in-order traversal of the tree, which returns a sorted list of the elements - I'm assuming that you're interested in a list as the output, because of the base case shown in the question. Try something like this:

(define (tree-sort tree)
  (if (empty-tree? tree)
      '()
      (append (tree-sort (left-subtree tree))
              (list (value tree))
              (tree-sort (right-subtree tree)))))

Use the appropriate procedures for testing if the tree is empty and for accessing each node's value, left and right subtrees. The above procedure will return a sorted list with the trees' values.