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aoc-racket/2017/d05/main.rkt

20 lines
575 B
Racket

#lang reader "../aoc-lang.rkt"
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(provide (rename-out [#%mb #%module-begin]))
(define-macro (#%mb (STARS) (JMP) ...)
#`(#%module-begin
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(time (escape (list->vector '(JMP ...)) 'STARS))))
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(define (escape vec stars)
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(let/ec exit
(for/fold ([pos 0])
([i (in-naturals)])
(unless (<= 0 pos (sub1 (vector-length vec)))
(exit i))
(define jmp (vector-ref vec pos))
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(vector-set! vec pos ((if (and (eq? stars '★★) (>= jmp 3))
sub1
add1) jmp))
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(+ pos jmp))))