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