From: Ramakrishnan Muthukrishnan <vu3rdd@gmail.com>
Date: Sun, 12 Sep 2010 18:11:46 +0000 (+0530)
Subject: solutions to 2.{64,65,66}
X-Git-Url: https://git.rkrishnan.org/listings/index.html?a=commitdiff_plain;h=bfdca48dadb73362e2ce28314c7138986110e236;p=sicp.git

solutions to 2.{64,65,66}
---

diff --git a/src/sicp/ex2_64.clj b/src/sicp/ex2_64.clj
new file mode 100644
index 0000000..ad581f8
--- /dev/null
+++ b/src/sicp/ex2_64.clj
@@ -0,0 +1,38 @@
+(ns sicp.ex2_64
+  (:use [sicp.ch2_3 :only (make-tree)]))
+
+(declare partial-tree)
+
+(defn list->tree [elements]
+  (first (partial-tree elements (count elements))))
+
+(defn partial-tree [elts n]
+  (if (= n 0)
+    (cons '() elts)
+    (let [left-size     (quot (- n 1) 2)
+          left-result   (partial-tree elts left-size)
+          left-tree     (first left-result)
+          non-left-elts (rest left-result)
+          right-size    (- n (+ left-size 1))
+          this-entry    (first non-left-elts)
+          right-result  (partial-tree (rest non-left-elts) right-size)
+          right-tree    (first right-result)
+          remaining-elts (rest right-result)]
+      (cons (make-tree this-entry
+                       left-tree
+                       right-tree)
+            remaining-elts))))
+
+(comment
+  "partial-tree divides the input sequence roughly into 2 halfs and creates a tree of
+   partial-trees on each of the branches."
+  "The tree for the input '(1 3 5 7 9 11) looks like this:"
+  "
+          5
+        /   \
+       1     9
+        \   / \
+         3 7   11
+  "
+  "partial-tree does a cons for every element of the list. So, order of growth is O(n)."
+)
\ No newline at end of file
diff --git a/src/sicp/ex2_65.clj b/src/sicp/ex2_65.clj
new file mode 100644
index 0000000..918f958
--- /dev/null
+++ b/src/sicp/ex2_65.clj
@@ -0,0 +1,16 @@
+(ns sicp.ex2_65
+  (:use [sicp.ex2_63]
+        [sicp.ex2_64]
+        [sicp.ex2_62 :only (union-set)]
+        [sicp.ch2_3  :only (intersection-set)]))
+
+(defn union-set-tree [set1 set2]
+  (let [ls1 (tree->list-1 set1)
+        ls2 (tree->list-1 set2)]
+    (list->tree (union-set ls1 ls2))))
+
+
+(defn intersection-set-tree [set1 set2]
+  (let [ls1 (tree->list-1 set1)
+        ls2 (tree->list-1 set2)]
+    (list->tree (intersection-set ls1 ls2))))
\ No newline at end of file
diff --git a/src/sicp/ex2_66.clj b/src/sicp/ex2_66.clj
new file mode 100644
index 0000000..9185621
--- /dev/null
+++ b/src/sicp/ex2_66.clj
@@ -0,0 +1,9 @@
+(ns sicp.ex2_66)
+
+(defn lookup [given-key set-of-records]
+  (if (empty? set-of-records)
+    false
+    (let [record (entry set-of-records)]
+      (cond (= given-key (get-key record)) record
+            (< given-key (get-key record)) (lookup given-key (left-branch set-of-records))
+            (> given-key (get-key record)) (lookup given-key (right-branch set-of-records))))))
\ No newline at end of file