1 #lang racket
2
3 ;;;;;;;;;;;;;;;;;;;;;;;;;;;
2.33
4 (define (accumulate op initial sequence)
5 (
if (
null?
sequence)
6 initial
7 (op (car sequence)
8 (accumulate op initial (cdr sequence)))))
9
10 (define (my-
map p sequence)
11 (accumulate (lambda (x y)
12 (cons (p x) y))
'() sequence))
13
14 (define (my-
append seq1 seq2)
15 (accumulate cons seq2 seq1))
16
17 (define (my-
length sequence)
18 (accumulate (lambda (x y) (+
1 y))
0 sequence))
19
20 ;;;;;;;;;;;;test
21 (my-map (lambda (x) (* x x)) (list
1 2 3))
22
23 (my-append (list
1 2 3) (list
4 5 6))
24
25 (my-length (list
1 2 3 4 5))
26
27 ;;;;;;;;;;;;;;;;;;;;;;;;;
2.34
28 (define (horner-eval x coefficient-
sequence)
29 (accumulate (lambda (
this-coeff higher-
terms)
30 (+
this-coeff (* x higher-
terms)))
31 0
32 coefficient-
sequence))
33
34 ;;;;;;;;;;test
35 (horner-eval
2 (list
1 3 0 5 0 1))
36
37 ;;;;;;;;;;;;;;;;;;;;;;;;
2.35
38 (define (count-
leaves tree)
39 (accumulate +
0 (map (lambda (node)
40 (
if (pair?
node)
41 (count-
leaves node)
42 1))
43 tree)))
44
45 ;;;;;;;;;;;;test
46 (count-leaves (list
'(1 2 3) '(
2 3 4)
4 5))
47
48 ;;;;;;;;;;;;;;;;;;;;
2.36
49 (define (accumulate-
n op init seqs)
50 (
if (
null?
(car seqs))
51 '()
52 (cons (accumulate op init (map car seqs))
53 (accumulate-
n op init (map cdr seqs)))))
54
55 ;;;;;;;;;;;;test
56 (define seqs (list
'(1 2 3) '(
4 5 6)
'(7 8 9) '(
10 11 12)))
57 (accumulate-n +
0 seqs)
58
59 ;;;;;;;;;;;;;;;;;;;;
2.37
60 (define (dot-
product v1 v2)
61 (accumulate +
0 (map *
v1 v2)))
62
63 (define (matrix-*-
vector m v)
64 (map (lambda (x) (dot-
product x v)) m))
65
66 (define (matrix-*-
matrix m n)
67 (let ((n-
cols (transpose n)))
68 (map (lambda (m-
row)
69 (map (lambda (n-
col)
70 (dot-product m-row n-
col))
71 n-
cols))
72 m)))
73
74 (define (transpose mat)
75 (accumulate-n cons
'() mat))
76
77 (define matrix1 (list
'(1 2 3) '(
1 9 3)
'(1 3 4)))
78 (define matrix2 (list
'(1 3 4) '(
3 4 5)
'(6 2 4)))
79 ;;;;;;;;;;;;test
80 (dot-product (list
1 1 1) (list
1 2 3))
81 (matrix-*-vector (list
'(1 2 3) '(
1 2 3)
'(1 3 3)) '(
2 3 4))
82 (matrix-*-
matrix matrix1 matrix2)
83
84 ;;;;;;;;;;;;;;;;;;;
2.38
85
86 (define (fold-
left op initial sequence)
87 (define (iter result rest)
88 (
if (
null?
rest)
89 result
90 (iter (op result (car rest))
91 (cdr rest))))
92 (iter initial sequence))
93
94 (define (fold-
right op initial sequence)
95 (accumulate op initial sequence))
96
97 ;;;;;;;;;;;;;;;test
98 (fold-right /
1 (list
1 2 3))
99 (fold-left /
1 (list
1 2 3))
100 (fold-right list
'() (list 1 2 3))
101 (fold-left list
'() (list 1 2 3))
102 ;;;;;;;;;;;用cons或list这些将产生不同结果
103 ;;;;;;;;;;;要使用那些在操作数互换位置后意义相同的。
104
105 ;;;;;;;;;;;;;;;;;;
2.39
106
107 (define (reverse1 sequence)
108 (fold-
right (lambda (x y)
109 (append y (list x)))
'() sequence))
110
111 (define (reverse2 sequence)
112 (fold-
left (lambda (x y)
113 (append (list y) x))
'() sequence))
114
115 ;;;;;;;;;;;;test
116 (reverse1 (list
1 2 3 4 6 8 9))
117 (reverse2 (list
1 2 3 4 7 8 5))
终于会一点了
需要复习线性代数了，感觉白学了！
转载于:https://www.cnblogs.com/tclan126/p/6411812.html
相关资源：数据结构—成绩单生成器
