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62 lines
2.2 KiB
Racket
62 lines
2.2 KiB
Racket
4 years ago
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#lang br
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(require racket/file rackunit racket/set)
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(define ints (map string->number (regexp-match* #rx"." "389547612")))
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(struct cup (val prev next) #:mutable)
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(define (link-cups! left right)
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(set-cup-next! left right)
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(set-cup-prev! right left))
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(define (find-cup cups dest-val)
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(for/first ([c (in-list cups)]
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#:when (eq? (cup-val c) dest-val))
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c))
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(define (next-cups start count)
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(cdr (reverse (foldl (λ (val acc) (cons (cup-next (car acc)) acc))
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(list start)
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(range count)))))
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(define (solve ints [max-int 9] [turns 100] [string-result? #true])
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(define cups (let* ([ints (if (= max-int (apply max ints))
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ints
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(append ints (for/list ([i (in-range 1 (add1 max-int))]
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#:unless (memq i ints))
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i)))]
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[cups (for/list ([int ints])
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(cup int #f #f))])
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(for-each link-cups! cups (append (cdr cups) (list (car cups))))
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cups))
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(define min-cup-val (apply min ints))
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(define max-cup-val max-int)
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(for/fold ([current (car cups)]
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#:result (void))
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([turn (in-range turns)])
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(match-define (list cup1 cup2 cup3 cup4) (next-cups current 4))
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(link-cups! current cup4)
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(define dest-cup (let ([pickup-vals (map cup-val (list cup1 cup2 cup3))])
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(let loop ([dest (sub1 (cup-val current))])
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(cond
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[(< dest min-cup-val) (loop max-cup-val)]
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[(memq dest pickup-vals) (loop (sub1 dest))]
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[else (find-cup cups dest)]))))
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(define dest-cup-next (cup-next dest-cup))
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(link-cups! dest-cup cup1)
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(link-cups! cup3 dest-cup-next)
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(cup-next current))
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(if string-result?
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(string-append*
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(for/list ([cup (next-cups (find-cup cups 1) (sub1 (length cups)))])
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(~a (cup-val cup))))
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(apply * (map cup-val (next-cups (find-cup cups 1) 2)))))
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(check-equal? (solve ints) "45286397")
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;; brutality won't be fast enough, but it was worth trying
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#;(solve ints 1000000 10000000 #f)
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