;; the birthday problem

;; initialize a vector of 365 false (or empty) pigeon holes
(define bdv (make-vector 365 false))

;; check off birthdays (by replacing falses with trues) until we get a
;; repeat, counting how many times it takes
(define (iterate counter)
  (let*
      ((r (random (vector-length bdv))))
    (begin
      (display "Random day: ")
      (display r)
      (newline)
      (if (vector-ref bdv r) 
          (begin
            (display "Done!")
            (newline)
            (display "It took ")
            (display counter)
            (display " times before a birthday was repeated")
            counter)
          (begin
            (vector-set! bdv r true)
            (iterate (+ 1 counter)))))))

(define (bd-prob) 
  (begin
    (vector-fill! bdv false)
    (iterate 0)))