solution to 2.63.

diff --git a/src/sicp/ex2_63.clj b/src/sicp/ex2_63.clj
new file mode 100644 (file)
index 0000000..0da2210
--- /dev/null
+++ b/src/sicp/ex2_63.clj
@@ -0,0 +1,43 @@
+(ns sicp.ex2_63
+  (:use [sicp.ch2_3 :only (entry left-branch right-branch)]
+        [clojure.test]))
+
+(defn tree->list-1 [tree]
+  (if (empty? tree)
+    '()
+    (concat (tree->list-1 (left-branch tree))
+            (cons (entry tree)
+                  (tree->list-1 (right-branch tree))))))
+
+(defn tree->list-2 [tree]
+  (let [copy-to-list (fn f [tree result-list]
+                       (if (empty? tree)
+                         result-list
+                         (f (left-branch tree)
+                            (cons (entry tree)
+                                  (f (right-branch tree) result-list)))))]
+    (copy-to-list tree '())))
+
+(deftest test-for-some-trees
+  (are [x y] [= x y]
+       (tree->list-1 '(7 (3 (1 ()) (5 ())) (9 () (11 ())))) '(1 3 5 7 9 11)
+       (tree->list-2 '(7 (3 (1 ()) (5 ())) (9 () (11 ())))) '(1 3 5 7 9 11)
+       (tree->list-1 '(3 (1 () ()) (7 (5 () ()) (9 () (11 () ()))))) '(1 3 5 7 9 11)
+       (tree->list-2 '(3 (1 () ()) (7 (5 () ()) (9 () (11 () ()))))) '(1 3 5 7 9 11)
+       (tree->list-1 '(5 (3 (1 () ()) ()) (9 (7 () ()) (11 () ())))) '(1 3 5 7 9 11)
+       (tree->list-2 '(5 (3 (1 () ()) ()) (9 (7 () ()) (11 () ())))) '(1 3 5 7 9 11)))
+
+;;;; part a
+(comment
+  "yes, as the above tests show, they add elements into the list in the same order
+   and hence produce same lists."
+)
+
+;;;; part b
+(comment
+  "tree->list-1 does a cons and an append of two lists at every step. The depth of the
+   tree is log(n). append grows as length of the list. The number of steps required to
+   traverse down to the tree is log(n). So, this is a O(n.log(n)) operation."
+
+  "list->tree-2 does only a cons operation at every step. So this is a O(n) operation."
+)