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aoc-racket/2016/day05.rkt

42 lines
1.8 KiB
Racket

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#lang br/quicklang
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(require openssl/md5)
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(define (read-syntax path port)
(strip-bindings
#`(module mod "day05.rkt"
(solve #,(string-trim (port->string port))))))
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(module+ reader (provide read-syntax))
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(provide #%module-begin)
(define (solve key)
(define-values
(part-a-solution part-b-solution)
(for*/fold ([part-a empty]
[part-b (make-vector 8 #f)])
([idx (in-naturals 1000000)]
[this-key (in-value (format "~a~a" key idx))]
#:break (and (= 8 (length part-a))
(andmap string? (vector->list part-b))))
(define this-hash (md5 (open-input-string this-key)))
(define next-part-a
(if (and (not (= 8 (length part-a)))
(string-prefix? this-hash "00000"))
(let ([next-str (substring this-hash 5 6)])
(displayln (format "part a progress: ~a" next-str))
(cons next-str part-a))
part-a))
(define next-part-b
(let ()
(when (and (string-prefix? this-hash "00000")
(string->number (substring this-hash 5 6))
(<= 0 (string->number (substring this-hash 5 6)) 7)
(not (vector-ref part-b (string->number (substring this-hash 5 6)))))
(displayln (format "part b progress: idx ~a, hash ~a, ~a at ~a" idx this-hash (substring this-hash 6 7) (substring this-hash 5 6)))
(vector-set! part-b (string->number (substring this-hash 5 6)) (substring this-hash 6 7)))
part-b))
(values next-part-a next-part-b)))
(displayln (format "part a: ~a" (apply string-append (reverse part-a-solution))))
(displayln (format "part b: ~a" (apply string-append (vector->list part-b-solution)))))
(provide solve)