問題文 🔗
Design a function called odd-from-n that consumes a natural number n, and produces a list of all
the odd numbers from n down to 1.
Note that there is a primitive function, odd?, that produces true if a natural number is odd.
問題文のリンク はこちら。
解答 🔗
;; Number -> ListOfNatural
;; produces a list of the odd numbers from n down to 1
;; (define (odd-from-n n) (cons 1 empty)) ; stub
(check-expect (odd-from-n 0) empty)
(check-expect (odd-from-n 2) (cons 1 empty))
(check-expect (odd-from-n 3) (cons 3 (cons 1 empty)))
(define (odd-from-n n)
(cond
[(= n 0) empty]
[(= n 1) (cons 1 empty)]
[(odd? n) (cons n (odd-from-n (sub1 n)))]
[else (odd-from-n (sub1 n))]))
メモ 🔗
odd?で奇数かどうかを判定できる