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23 lines
821 B
Racket
23 lines
821 B
Racket
7 years ago
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#lang br/quicklang
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(require sugar/list)
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(module+ reader
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(require syntax/strip-context)
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(provide read-syntax)
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(define (read-syntax path port)
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(strip-context #`(module day1 aoc-racket/2017/d1
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#,@(for/list ([datum (in-port read port)])
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datum)))))
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(provide (rename-out [mb #%module-begin]))
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(define-macro (mb SELECTOR CAPTCHA-STR ...)
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#'(#%module-begin (captcha-sum 'SELECTOR CAPTCHA-STR) ...))
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(define (captcha-sum offset-sig num)
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(define digits (for/list ([c (in-string (number->string num))])
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(string->number (string c))))
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(define offset (if (eq? offset-sig '★) -1 (/ (length digits) 2)))
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(for/sum ([first (in-list digits)]
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[second (in-list (shift-cycle digits offset))]
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#:when (= first second))
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first))
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