60 lines
1.9 KiB
Racket
60 lines
1.9 KiB
Racket
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#lang curly-fn racket
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(require "../lib.rkt")
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(define (parse-rule rule)
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(match rule
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[(regexp #px"(\\d+): (.+)" (list _ rule alts))
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(cons (string->number rule)
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(~>> alts
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(string-replace _ "|" ")(")
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(format "((~a))")
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open-input-string
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read))]))
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(define-values (rules msgs)
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(match-let ([(list rules msgs) (problem-input-grouped 19)])
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(values (make-hash (map parse-rule (string-lines rules)))
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(string-lines msgs))))
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(define (ruleset start)
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(list->set
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;; loop: number? -> (listof string?)
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(let loop ([rule start])
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(apply append
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(map #{match %
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[`(,l) #:when (string? l) %]
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[`(,rs ...) (map #{apply string-append %}
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(apply cartesian-product
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(map #{loop %} rs)))]}
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(hash-ref rules rule))))))
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(define rule42 (ruleset 42))
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(define rule31 (ruleset 31))
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(define len (string-length (set-first rule42)))
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(define (string-group len str)
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(for/list ([group (/ (string-length str) len)])
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(substring str (* group len) (* (add1 group) len))))
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(define (matches-rules-1 str)
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(and (= (string-length str) (* 3 len))
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(let ([strs (string-group len str)])
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(and (set-member? rule42 (first strs))
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(set-member? rule42 (second strs))
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(set-member? rule31 (third strs))))))
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(define (matches-rules-2 str)
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(and (zero? (remainder (string-length str) len))
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(let* ([strs (string-group len str)]
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[count (length strs)])
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(for/or ([c (in-range (add1 (floor (/ count 2))) count)])
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(and (andmap #{set-member? rule42 %} (take strs c))
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(andmap #{set-member? rule31 %} (drop strs c)))))))
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(define-values (part1 part2)
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(values (count #{matches-rules-1 %} msgs)
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(count #{matches-rules-2 %} msgs)))
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(show-solution part1 part2)
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