added: 14-18 execrise

code/sector1/1_12.rkt

@@ -1,7 +1,6 @@
 (define (pascal row col)
     (cond ((> col row)
             (error "unvalid col value"))
-          ((or (= col 0) (= row col))
-            1)
+          ((or (= col 0) (= row col) 1))
           (else (+ (pascal (- row 1) (- col 1))
                    (pascal (- row 1) col)))))

code/sector1/1_14.rkt

@@ -0,0 +1,16 @@
+
+
+
+                                          count-change 11
+                                        <-                  ->
+                             count-change(10)       count-change(1)
+                             <-           ->
+                            cc(5)       cc(0)
+                           <-   -> 
+                        cc(1)     cc(4)
+                                    ->
+                                     cc(3)
+                                         ->
+                                         cc(2)
+                                          -> 
+                                          cc(1)

code/sector1/1_16.rkt

@@ -0,0 +1,7 @@
+(define (even? n)
+    (= (reminder n 2) 0))
+
+(define (make-mod  b n a )
+    (cond ((= n 0) a)
+        ((even? n)  (square(fast-expt  b (/  n 2) a)) )
+        (else  (*  b  (fast-expt b  (- n 1)) a) )))

code/sector1/1_17.rkt

@@ -0,0 +1,11 @@
+(define (double n)
+    n + n)
+
+(define (havle n)
+   (cond ((even? n) (/ n 2) )))
+
+
+(define (make-multi  a b  )
+    (cond ((= b 0) 0)
+        ((even?  b )  (double(make-multi  a (havle b ) )) )
+        (else  (+  a  (make-multi a  (- b 1))) )))

code/sector1/1_18.rkt

@@ -0,0 +1,14 @@
+(define (multi a b)
+    (multi-iter a b 0))
+
+(define (multi-iter a b product)
+    (cond ((= b 0)
+            product)
+          ((even? b)
+            (multi-iter (double a)
+                        (halve b)
+                        product))
+          ((odd? b)
+            (multi-iter a
+                        (- b 1)
+                        (+ a product)))))