#lang racket
;;;;;;;;;;;;;;;;;;;;;;;;2.17
(define (last-
pair L)
(if (
null?
(cdr L))
L
(last-
pair (cdr L))))
;;;;;;;;;;;;;;;;;;;;;;;2.18
(define (reverse L)
(if (
null?
(cdr L))
L
(cons (reverse (cdr L)) (car L))))
;;;;;;;;;;;;;;;;;;;;;;2.19
(define us-coins (list
50 25 10 5 1))
(define us-coins2 (list
1 5 10 25 50))
(define uk-coins (list
100 50 20 10 5 2 1))
(define (cc amount coin-
values)
(cond ((= amount
0)
1)
((or (< amount
0) (no-more? coin-values))
0)
(else
(+
(cc amount
(except-first-denomination coin-
values))
(cc (-
amount
(first-denomination coin-
values))
coin-
values)))))
(define (no-more?
coins)
(null?
coins))
(define (except-first-denomination coin-
values)
(cdr coin-
values))
(define (first-
denomination coins)
(car coins))
;;;;;;;;;;;;;;;;;;;;2.20
(define (same-
parity sample . others)
(filter (if (even?
sample)
even?
odd?
)
(cons sample others)))
;;;;;;;;;;;;;;;;;;;;;;;test
;(last-pair (list
23 37 149 34))
;(reverse (list 1 4 9 16 25))
;(cc 100 us-
coins)
;(cc 100 us-
coins2)
;(same-parity
2 3 4 5 6 7)
转载于:https://www.cnblogs.com/tclan126/p/6390234.html
