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#lang racket
(define/contract (rotated-digits max-n)
(-> exact-integer? exact-integer?)
(for/fold ([good-number-count 0])
([n (in-range 1 (add1 max-n))])
(if (is-good? n)
(add1 good-number-count)
good-number-count)))
(define/contract (is-good? test-number)
(-> exact-integer? boolean?)
(define test-string (number->string test-number))
(match test-string
[(regexp #rx"^[018]*$") #false]
[(regexp #rx"^[0125689]*$") #true]
[_ #false]))
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