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13 lines
471 B
Racket
13 lines
471 B
Racket
#lang reader "../aoc-lang.rkt"
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(provide (rename-out [#%mb #%module-begin]))
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(define-macro (#%mb (STARS) (NUMBER) ...)
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#'(#%module-begin (captcha-sum 'STARS NUMBER) ...))
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(define (captcha-sum stars num)
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(define digits (number->digits num))
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(define offset (if (eq? stars '★) -1 (quotient (length digits) 2)))
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(for/sum ([digit (in-list digits)]
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[other-digit (in-list (shift-cycle digits offset))]
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#:when (= digit other-digit))
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digit)) |