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aoc-racket/2017/d19/main.rkt

40 lines
1.6 KiB
Racket

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#lang br/quicklang
(require "../helper.rkt")
(provide read-syntax (rename-out [#%mb #%module-begin]) ★★)
(define (read-syntax path port)
(define lines (port->lines port))
(strip-context #`(module mod "main.rkt"
#,@(for/list ([datum (in-port read (open-input-string (car lines)))])
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datum)
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#,@(cdr lines))))
(define-macro (#%mb STARS LINE ...)
#'(#%module-begin
(time (STARS (list LINE ...)))))
(define (traverse lines #:count-steps [count-steps? #f])
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(define chars (for*/hasheqv ([(line lidx) (in-indexed lines)]
[(c cidx) (in-indexed (string->list line))]
#:unless (char=? c #\space))
(values (+ lidx (* +i cidx)) c)))
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(define start (for/first ([k (in-hash-keys chars)]
#:when (zero? (real-part k)))
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k))
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(define down 1) (define up -1) (define left -i) (define right +i)
(let loop ([here start][dir down][path null])
(define here-char (hash-ref chars here #f))
(cond
[here-char
(define next-dir (if (char=? here-char #\+)
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(if (hash-has-key? chars (+ here (* dir right))) (* dir right) (* dir left))
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dir))
(loop (+ here next-dir) next-dir (cons here-char path))]
[count-steps? (length path)]
[else (list->string (filter char-alphabetic? (reverse path)))])))
(define ( lines) (traverse lines))
(define (★★ lines) (traverse lines #:count-steps #t))