doctor-away.scm

(define (doctor-away-numbers? a b c)
  (let ((b1 (div b 10))
	(b2 (mod b 10))
	(c1 (div c 10))
	(c2 (mod c 10)))
    (and (= (+ (* (div b2 a) 10)
	       (/ (+ (* b1 10) (div b2 a)) a))
	    c)
	 (= (apply +
		   (append
		    (make-list c1 a)
		    (make-list c2 a)))
	    b)
	 (= (+ (* c1 a) (* c2 a))
	    b))))

(let loop ((a 1) (b 10) (c 10) (ans '()))
  (cond [(= a 10) ans]
	[(= b 100) (loop (+ a 1) 10 10 ans)]
	[(= c 100) (loop a (+ b 1) 10 ans)]
	[else (loop a b (+ c 1) (if (doctor-away-numbers? a b c)
				    (cons `(,a ,b ,c) ans)
				    ans))]))