d09 p1 (slow)

master
Matthew Butterick 6 years ago
parent 0adb204517
commit 214186f3f8

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10 players; last marble is worth 1618 points

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#lang debug br
(require racket/file)
(define ()
(match-define (list player-count marble-count)
(map string->number (regexp-match* #px"\\d+" (file->string "09.txt"))))
(define scores (make-hasheqv))
(let loop ([marble 1] [pos 0] [circle (list 0)])
(cond
[(> marble marble-count) (argmax cdr (hash->list scores))]
[(zero? (modulo marble 23))
(define len (length circle))
(define deletion-pos (modulo (+ (- pos 7) len) len))
(define-values (head tail) (split-at circle deletion-pos))
(define player (modulo marble player-count))
(hash-update! scores player (λ (sc) (+ marble (car tail) sc)) 0)
(loop (add1 marble) deletion-pos (append head (cdr tail)))]
[else
(define next-pos (add1 (modulo (add1 pos) (length circle))))
(define-values (head tail) (split-at circle next-pos))
(loop (add1 marble) next-pos (append head (list marble) tail))])))
#;(define (★★)
)
#;(★★)
#;(module+ test
(require rackunit)
(check-equal? (time ()) 437654)
(check-equal? (time (★★)) 566))

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400 players; last marble is worth 71864 points