Self-describing numbers: Difference between revisions

=={{header|Racket}}==

<lang Racket>#lang racket

(define (get-digits number (lst null))

(if (zero? number)

lst

(get-digits (quotient number 10) (cons (remainder number 10) lst))))

(define (self-describing? number)

(define digits (get-digits number))

(for/fold ((bool #t))

((i (in-range (length digits))))

(and bool

(= (count (lambda (x) (= x i)) digits)

(list-ref digits i)))))</lang>

Sadly, the implementation is too slow for the optional task, taking somewhere around 3 minutes to check all numbers below 100.000.000