category

1 files changed, 134 insertions, 0 deletions

diff --git a/Computer_Science/SICP/ch2_2_2.scm b/Computer_Science/SICP/ch2_2_2.scm
new file mode 100644
index 0000000..fbcf46d
--- /dev/null
+++ b/Computer_Science/SICP/ch2_2_2.scm
@@ -0,0 +1,134 @@
+(define x (cons (list 1 2) (list 3 4)))
+
+(define (length x)
+  (cond ((null? x) 0)
+        ((not (pair? x)) 1)
+        (else (+ (length (cdr x)) 1))))
+
+(define (count-leaves x)
+  (cond ((null? x) 0)
+        ((not (pair? x)) 1)
+        (else (+ (count-leaves (car x))
+                 (count-leaves (cdr x))))))
+
+(length x)
+(count-leaves x)
+
+;; Exercise 2.24
+;; Length is wrong !!!
+;; (car (cdr )) to get the left leaf
+
+(define list-1 (list 1 (list 2 (list 3 4))))
+(length list-1)
+(count-leaves list-1)
+
+;; Exercise 2.25
+(car (cdr (car (cdr (cdr (list 1 3 (list 5 7) 9))))))
+(car (car (list (list 7))))
+(car (cdr (car (cdr (car (cdr (car (cdr (car (cdr (car (cdr (list 1 (list 2 (list 3 (list 4 (list 5 (list 6 7))))))))))))))))))
+
+;; Exercise 2.26
+(define z (list 1 1 1))
+(define x (list 1 2 3))
+(define y (list 4 5 6))
+
+(append x y)
+(car (car (cons x y)))
+(car (car (list x y)))
+
+(car (cdr (cons x y)))
+(car (car (cdr (list x y))))
+
+;; Exercise 2.27
+
+!!! ;; Exercise2.18
+(define (reverse items)
+  (if (null? (cdr items))
+    items
+    (append (reverse (cdr items))
+            (cons (car items) nil))))
+
+(define (deep-reverse items)
+  (if (null? (cdr items))
+    (if (not (pair? (car items)))
+      items
+      (cons (deep-reverse (car items)) nil))
+    (append (cond ((pair? (cdr items)) 
+                   (deep-reverse (cdr items)))
+                  ((pair? (car (cdr items)))
+                   (cons (deep-reverse (car (cdr items))) nil))
+                  ;; Some problem in else.
+                  (else (deep-reverse (cdr items))))
+            (cond ((pair? (car items))
+                   (cons (deep-reverse (car items)) nil))
+                  (else (cons (car items) nil))))))
+
+(define y
+  (list (list 1 2) (list 3 4) (list 5 6)))
+
+(define z (list (list 1 2)))
+(deep-reverse z)
+(reverse z)
+
+(reverse y)
+(deep-reverse y)
+
+(cons (deep-reverse (car (list (list 1 2)))) nil)
+
+(deep-reverse 
+  (list 1 (list 2 3) 4 (list 5 6)))
+
+(define x
+  (list (list 1 2) (list 3 4)))
+(list (list 1 2) (list 3 4))
+(reverse x)
+(deep-reverse x)
+(deep-reverse (list 3 4))
+(deep-reverse (list 1 2 3))
+(reverse (list 1 2 3))
+
+;; Exercise2.28
+
+(define (fringe items)
+  (if (not (pair? items))
+    (list items)
+    (append (fringe (car items))
+            (if (null? (cdr items))
+              nil
+              (fringe (cdr items))))))
+
+
+(append (list 3) (list 4))
+(append (list 4) nil)
+(append nil (list 4))
+(list 4)
+(list 3 4)
+(list nil)
+(append (list nil) (list nil))
+
+(define x
+  (list (list 1 2) (list 3 4)))
+(fringe x)
+(fringe (list x x))
+(list 1 2 3 4)
+(list 1 2 3 4 1 2 3 4)
+
+(append (list 2) (list 3))
+(list 2 3)
+(list (list 1 2) (list 3 4))
+(list (list 1 2) 3 4)
+
+;; Exercise2.29
+
+(define (make-mobile left right)
+  (list left right))
+
+(define (make-branch length structure)
+  (list length structure))
+
+(define (left-branch mobile)
+  (car (mobile)))
+(define (right-branch mobile)
+  (cdr (mobile)))
+
+(define branch-length)