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#lang br/quicklang ;; http://adventofcode.com/2016/day/14
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(require openssl/md5)
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(provide read-syntax
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(rename-out [mb #%module-begin]))
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(define (read-syntax path port)
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(strip-bindings
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#`(module mod "lang.rkt"
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#,(string-trim (port->string port)))))
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(define-macro (mb SALT)
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#'(#%module-begin
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(solve SALT)
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(parameterize ([key-stretch 2017])
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(solve SALT))))
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(define key-stretch (make-parameter 0))
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(require sugar/cache)
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(define/caching (get-hash salt i)
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(for/fold ([str (string-downcase (format "~a~a" salt i))])
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([i (in-range (key-stretch))])
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(md5 (open-input-string str))))
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(define (valid? hash salt i)
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(let* ([triple-char-pat (pregexp "(.)\\1\\1")]
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[result (regexp-match triple-char-pat hash)])
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(and result
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(let* ([repeated-char (cadr result)]
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[penta-char-pat (pregexp (format "(~a)\\1\\1\\1\\1" repeated-char))])
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(for/or ([idx (in-range (add1 i) (+ 1001 i))])
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(regexp-match penta-char-pat (get-hash salt idx)))))))
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(define (solve salt)
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(caar
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(for/fold ([keys empty])
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([i (in-naturals)]
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#:break (= (length keys) 64))
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(define hash (get-hash salt i))
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(if (valid? hash salt i)
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(report* i hash (cons (cons i hash) keys))
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keys))))
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