You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
18 lines
705 B
Racket
18 lines
705 B
Racket
#lang br
|
|
(require racket/file rackunit)
|
|
|
|
(define (solve str max-turns)
|
|
(define nums (map string->number (string-split str ",")))
|
|
(define previously-seen (make-hasheq))
|
|
(for ([(num turn) (in-indexed (drop-right nums 1))])
|
|
(hash-set! previously-seen num (add1 turn)))
|
|
(for/fold ([last-seen (last nums)])
|
|
([turn (in-range (add1 (length nums)) (add1 max-turns))])
|
|
(begin0
|
|
(match (hash-ref previously-seen last-seen #false)
|
|
[#false 0]
|
|
[where-previously-seen (- (sub1 turn) where-previously-seen)])
|
|
(hash-set! previously-seen last-seen (sub1 turn)))))
|
|
|
|
(check-equal? (solve "11,0,1,10,5,19" 2020) 870)
|
|
(check-equal? (solve "11,0,1,10,5,19" 30000000) 9136) |