Data commit

Task/Tree-traversal/Racket/tree-traversal.rkt

@@ -0,0 +1,25 @@
+#lang racket
+
+(define the-tree ; Node: (list <data> <left> <right>)
+  '(1 (2 (4 (7 #f #f) #f) (5 #f #f)) (3 (6 (8 #f #f) (9 #f #f)) #f)))
+
+(define (preorder tree visit)
+  (let loop ([t tree])
+    (when t (visit (car t)) (loop (cadr t)) (loop (caddr t)))))
+(define (inorder tree visit)
+  (let loop ([t tree])
+    (when t (loop (cadr t)) (visit (car t)) (loop (caddr t)))))
+(define (postorder tree visit)
+  (let loop ([t tree])
+    (when t (loop (cadr t)) (loop (caddr t)) (visit (car t)))))
+(define (levelorder tree visit)
+  (let loop ([trees (list tree)])
+    (unless (null? trees)
+      ((compose1 loop (curry filter values) append*)
+       (for/list ([t trees] #:when t) (visit (car t)) (cdr t))))))
+
+(define (run order)
+  (printf "~a:" (object-name order))
+  (order the-tree (?(x) (printf " ~s" x)))
+  (newline))
+(for-each run (list preorder inorder postorder levelorder))