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aoc-racket/2017/d1/main.rkt

18 lines
604 B
Racket

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#lang br/quicklang
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(require "../helper.rkt")
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(provide read-syntax)
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(define (read-syntax path port)
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(strip-context #`(module mod "main.rkt" #,@(port->datums port))))
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(provide (rename-out [#%mb #%module-begin]))
(define-macro (#%mb STARS NUMBER ...)
#'(#%module-begin (captcha-sum 'STARS NUMBER) ...))
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(define (captcha-sum stars num)
(define digits (number->digits num))
(define offset (if (eq? stars ') -1 (quotient (length digits) 2)))
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(for/sum ([digit (in-list digits)]
[other-digit (in-list (shift-cycle digits offset))]
#:when (= digit other-digit))
digit))