Binary tree inorder traversal Racket
Question
I am trying to write the algorithm for inorder traversal for a binary tree using RACKET/DR. RACKET
(define (print-records node number)
(cond
[(not (empty? node-left))(print-records (node-left node) number )]
*Do This before moving to next IF clause*
[(not (empty? node-right))(print-records(node-right node) number)]
))
I am trying to follow the following algorithm
InOrder(node)
if node is null return
InOrder(node.left)
Print(node)
InOrder(node.Right)
My problem is that through COND I can execute one expression and it will skip the rest. I tried to add two expressions under one it did not work either eg ((a)(b)). I also tried to make a helper procedure but that did not work either.
2 answers
solution1
2 ACCPTED 2013-05-16 22:03:18
You're using cond in a wrong way. Notice that you have to recursively traverse the left part of the tree, then visit the current node and then recursively traverse the right part of the tree - they're not mutually exclusive alternatives, the three steps need to be performed in precisely that order. Try something like this instead:
(define (print-records node number)
(unless (empty? (node-left node))
(print-records (node-left node) number))
(print (node-value node)) ; replace this line with the actual printing code
(unless (empty? (node-right node))
(print-records (node-right node) number)))
Some explanations:
-
(unless <condition> <body>)is just shorthand for(cond ((not <condition>) <body>)). - The real work of the traversal is done between the two recursive calls, in this case I wrote
(print (node-value node))as an example, replace that line with the actual printing code for the current node's value. - It's not clear what do you intend to do with the
numberparameter, as it is it's just being passed around, unused.
solution2
2 2013-05-16 23:14:53
Walking a binary-tree is a very general operation. You can make a general procedure and then specialize it with the function to apply to each node.
(define (walker node function)
(unless (empty? node)
(walker (node-left node) function)
(function node)
(walker (node-right node) function)))
Note: it is nice to check for empty? at the beginning of the function.
(define (print-records node number)
(walker node (compose print node-value))) ; ignore number, it seems.
You could also work this as:
(define (walking-with function)
(letrec ((walker (lambda (node)
(unless (empty? node)
(walker (node-left node))
(function node)
(walker (node-right node))))))
walker))
(define print-records-for (walking-with (compose print node-value)))
(print-records-for node)
> ...
The technical post webpages of this site follow the CC BY-SA 4.0 protocol. If you need to reprint, please indicate the site URL or the original address.Any question please contact:yoyou2525@163.com.