solutions

Exercise_246.rkt

@@ -0,0 +1,19 @@
+#lang racket
+
+(check-expect (extract < (cons 6 (cons 4 '())) 5) (list 4))
+(check-expect (extract > (cons 6 (cons 4 '())) 5) (list 6))
+
+(define (extract R l t)
+  (cond
+    [(empty? l) '()]
+    [else (cond
+            [(R (first l) t)
+             (cons (first l)
+                   (extract R (rest l) t))]
+            [else
+             (extract R (rest l) t)])]))
+
+
+(extract < (cons 6 (cons 4 '())) 5)
+
+(extract < (cons 4 '()) 5)

Exercise_247.rkt

@@ -0,0 +1,16 @@
+#lang racket
+
+(check-expect (extract < (cons 6 (cons 4 '())) 5) (list 4))
+(check-expect (extract > (cons 6 (cons 4 '())) 5) (list 6))
+
+(define (extract R l t)
+  (cond
+    [(empty? l) '()]
+    [else (cond
+            [(R (first l) t)
+             (cons (first l)
+                   (extract R (rest l) t))]
+            [else
+             (extract R (rest l) t)])]))
+
+(extract < (cons 8 (cons 4 '())) 5)

Exercise_248.rkt

@@ -0,0 +1,8 @@
+#lang racket
+(define (squared>? x c)
+  (> (* x x) c))
+
+
+(squared>? 3 10)
+
+(squared>? 4 10)

Exercise_249.rkt

@@ -0,0 +1,9 @@
+#lang racket
+
+(define (f x) x)
+
+(cons f '())
+
+(f f)
+
+(cons f (cons 10 (cons (f 10) '())))

Exercise_250.rkt

@@ -0,0 +1,40 @@
+#lang racket
+
+(check-within (tabulate sin 5) (tab-sin 5) 0.000001)
+(check-within (tabulate sqrt 5) (tab-sqrt 5) 0.000001)
+
+(define (tabulate g n)
+  (cond
+    [(= n 0) (list (g 0))]
+    [else
+     (cons
+      (g n)
+      (tabulate g (sub1 n)))]))
+
+
+(check-expect (tab-sqr 3) (list 9 4 1 0))
+
+(define (tab-sqr n)
+  (tabulate sqr n))
+
+(check-within (tab-tan 3) (list (tan 3) (tan 2) (tan 1) (tan 0)) 0.000001)
+
+(define (tab-tan n)
+  (tabulate tan n))
+
+
+(define (tab-sin n)
+  (cond
+    [(= n 0) (list (sin 0))]
+    [else
+     (cons
+      (sin n)
+      (tab-sin (sub1 n)))]))
+
+(define (tab-sqrt n)
+  (cond
+    [(= n 0) (list (sqrt 0))]
+    [else
+     (cons
+      (sqrt n)
+      (tab-sqrt (sub1 n)))]))

Exercise_251.rkt

@@ -0,0 +1,23 @@
+#lang racket
+
+(check-expect (fold1 '(1 2 3 4 5) 0 +) (sum '(1 2 3 4 5)))
+(check-expect (fold1 '(1 2 3 4 5) 1 *) (product '(1 2 3 4 5)))
+
+(define (fold1 l i g)
+  (cond
+    [(empty? l) i]
+    [else
+     (g (first l)
+        (fold1 (rest l) i g))]))
+
+
+(check-expect (fold1-sum '(1 2 3 4 5)) (+ 1 2 3 4 5))
+
+(define (fold1-sum l)
+  (fold1 l 0 +))
+
+
+(check-expect (fold1-product '(1 2 3 4 5)) (* 1 2 3 4 5))
+
+(define (fold1-product l)
+  (fold1 l 1 *))

Exercise_252.rkt

@@ -0,0 +1,32 @@
+#lang racket
+
+(define LO-N1 (list 1 2 3 4 5 6))
+(define LO-POSN1 (list (make-posn 20 30) (make-posn 40 70) (make-posn 50 50)))
+
+(define emt
+  (empty-scene 100 100))
+(define dot
+  (circle 3 "solid" "red"))
+
+
+(check-expect (fold2 LO-N1 1 *) (product LO-N1))
+(check-expect (fold2 LO-POSN1 emt place-dot) (image* LO-POSN1))
+
+(define (fold2 l i g)
+  (cond
+    [(empty? l) i]
+    [else
+     (g (first l)
+        (fold2 (rest l) i g))]))
+
+
+(check-expect (fold2-product LO-N1) (product LO-N1))
+
+(define (fold2-product l)
+  (fold2 l 1 *))
+
+
+(check-expect (fold2-image* LO-POSN1) (image* LO-POSN1))
+
+(define (fold2-image* l)
+  (fold2 l emt place-dot))

Exercise_253.rkt

@@ -0,0 +1,11 @@
+#lang racket
+
+(check-expect (number? 5) #true)
+
+(check-expect (equal? #true "abde") #false)
+
+(check-expect (+ 1 2 3) 6)
+
+(check-expect (list 5) (list 5))
+
+(check-expect (list? '(1 2 3 4)) #true)

Exercise_256.rkt

@@ -0,0 +1,4 @@
+#lang racket
+
+(check-expect (argmax second (list (list "a" 4) (list "b" 2) (list "c" 9) (list "d" 5)))
+              (list "c" 9))