gistfile1.sls

#lang racket

(define floors
  '((1 . 10)
    (2 . 3)
    (3 . 25)
    (4 . 100)))

(define (probability-list floors)
  (cond [(empty? floors) empty]
        [else (cons (cons (car (car floors))
                          (apply + (map cdr (cdr floors))))
                    (probability-list (cdr floors)))]))

(define (total floors)
  (apply + (map cdr floors)))

(define (match-floor num floors)
  (cond [(> num (cdr (car floors))) (car (car floors))]
        [else (match-floor num (cdr floors))]))

(define (choose-floor floors)
  (match-floor (random (total floors))
                (probability-list floors)))