問題文 🔗
Design a function that produces an image of the numbers from n to zero, side by side.
問題文のリンク はこちら。
解答 🔗
(define TEXT-SIZE 20)
(define TEXT-COLOR "black")
(define SPACING (text " " TEXT-SIZE TEXT-COLOR))
;; Natural -> Image
;; produce an image of n, n-1, ... 0 side by side
(check-expect (decreasing-image 0) (text "0" 20 "black"))
(check-expect (decreasing-image 3) (beside (text "3" 20 "black") SPACING
(text "2" 20 "black") SPACING
(text "1" 20 "black") SPACING
(text "0" 20 "black")))
;(define (decreasing-image n) empty-image) ; stub
(define (decreasing-image n)
(cond [(zero? n) (text "0" TEXT-SIZE TEXT-COLOR)]
[else
(beside (text (number->string n) TEXT-SIZE TEXT-COLOR)
SPACING
(decreasing-image (sub1 n)))]))
メモ 🔗
besideで Image を横に並べることができるsub1 nは(- n 1)と同じ