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38 lines
1.4 KiB
Racket
38 lines
1.4 KiB
Racket
#lang debug br
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(require racket/file)
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(define (nth-mpr mprs n)
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(for/fold ([mprs mprs])
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([i (in-range n)])
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(mcdr mprs)))
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(define (★)
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(match-define (list player-count max-marbles)
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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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(define circle (mcons #f (mcons 0 null)))
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(let loop ([marble 1] [marbles-in-circle 1] [pos 0])
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(cond
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[(> marble max-marbles) (cdr (argmax cdr (hash->list scores)))]
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[(zero? (modulo marble 23))
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(define deletion-pos (modulo (+ (- pos 7) marbles-in-circle) marbles-in-circle))
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(define last-left-mpr (nth-mpr circle deletion-pos))
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(define removed-marble (mcar (mcdr last-left-mpr)))
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(set-mcdr! last-left-mpr (mcdr (mcdr last-left-mpr)))
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(define player (modulo marble player-count))
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(hash-update! scores player (λ (sc) (+ removed-marble marble sc)) 0)
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(loop (add1 marble) (sub1 marbles-in-circle) deletion-pos)]
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[else
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(define next-pos (add1 (modulo (add1 pos) marbles-in-circle)))
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(define last-left-mpr (nth-mpr circle next-pos))
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(set-mcdr! last-left-mpr (mcons marble (mcdr last-left-mpr)))
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(loop (add1 marble) (add1 marbles-in-circle) next-pos)])))
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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)) |