From: Ramakrishnan Muthukrishnan <vu3rdd@gmail.com>
Date: Sun, 17 Oct 2010 19:17:56 +0000 (+0530)
Subject: solution to 2.34, 2.35, 2.36 and 2.37
X-Git-Url: https://git.rkrishnan.org/%5B/frontends/flags/%22news.html/nxhtml.html?a=commitdiff_plain;h=e2fa397aae723d9c5ea05890f1507c260641e04d;p=sicp.git

solution to 2.34, 2.35, 2.36 and 2.37
---

diff --git a/src/sicp/ex2_34.rkt b/src/sicp/ex2_34.rkt
new file mode 100644
index 0000000..aa671fe
--- /dev/null
+++ b/src/sicp/ex2_34.rkt
@@ -0,0 +1,10 @@
+#lang racket
+
+(require "utils.rkt")
+
+(define (horner-eval x coefficient-sequence)
+  (accumulate (lambda (this-coeff higher-terms) (+ (* x this-coeff) higher-terms))
+              0
+              coefficient-sequence))
+
+(horner-eval 2 '(1 3 0 5 0 1))
\ No newline at end of file
diff --git a/src/sicp/ex2_35.rkt b/src/sicp/ex2_35.rkt
new file mode 100644
index 0000000..23e7e09
--- /dev/null
+++ b/src/sicp/ex2_35.rkt
@@ -0,0 +1,8 @@
+#lang racket
+
+(require "utils.rkt")
+
+(define (count-leaves t)
+  (accumulate +
+              0
+              (map (lambda (x) (if (pair? x) (count-leaves x) 1)) t)))
\ No newline at end of file
diff --git a/src/sicp/ex2_36.rkt b/src/sicp/ex2_36.rkt
new file mode 100644
index 0000000..658b860
--- /dev/null
+++ b/src/sicp/ex2_36.rkt
@@ -0,0 +1,13 @@
+#lang racket
+
+(require "utils.rkt")
+
+(define (accumulate-n op init seqs)
+  (if (null? (car seqs))
+      '()
+      (cons (accumulate op init (map car seqs))
+            (accumulate-n op init (map cdr seqs)))))
+
+(provide accumulate-n)
+
+;; (accumulate-n + 0 '((1 2 3) (4 5 6) (7 8 9) (10 11 12)))
\ No newline at end of file
diff --git a/src/sicp/ex2_37.rkt b/src/sicp/ex2_37.rkt
new file mode 100644
index 0000000..841e6c2
--- /dev/null
+++ b/src/sicp/ex2_37.rkt
@@ -0,0 +1,24 @@
+#lang racket
+
+(require "utils.rkt"
+         "ex2_36.rkt")
+
+;; dot product
+(define (dot-product v w)
+  (accumulate + 0 (map * v w)))
+
+(define (matrix-*-vector m v)
+  (map (lambda (r) (dot-product r v)) m))
+
+;; (matrix-*-vector '((1 2 3 4) (4 5 6 6) (6 7 8 9)) '(1 2 3 4))
+
+(define (transpose m)
+  (accumulate-n cons '() m))
+
+;; (transpose '((1 2 3) (4 5 6) (7 8 9)))
+
+(define (matrix-*-matrix m n)
+  (let ([cols (transpose n)])
+    (map (lambda (v) (matrix-*-vector cols v)) m))) 
+
+;; (matrix-*-matrix '((0 -1 2) (4 11 2)) '((3 -1) (1 2) (6 1)))
\ No newline at end of file