ex-it
ex-it: string -> string
Change every “x” to a “y”.
(check-expect (ex-it "tresxxx") "tres")
(check-expect (ex-it "zyzzyva") "zyzzyva") ; no change
unlucky
unlucky: number -> number
How many multiples of 13 appear in the digits of n? (Just consider two digit multiples.)
(check-expect (unlucky 131) 1)
(check-expect (unlucky 139) 2)
(check-expect (unlucky 1263) 1)
(check-expect (unlucky 1326) 2)