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aoc-racket/2017/d01/main.rkt

13 lines
471 B
Racket

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