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#lang racket
(require advent-of-code)
(provide open-day
transpose
chunks-by)
(define (open-day n [year 2021])
(open-aoc-input (find-session) year n #:cache (string->path "./cache")))
(define (transpose xss)
(apply map list xss))
(define (chunks-by xs [by identity])
(define (do-chunks-by xs by group result)
(match* (xs group)
[('() _) (reverse (cons group result))]
[((list* h t) '()) (do-chunks-by t by (cons h group) result)]
[((list* h t) (list* g _))
#:when (equal? (by h) (by g))
(do-chunks-by t by (cons h group) result)]
[((list* h t) _) (do-chunks-by t by (list h) (cons group result))]))
(do-chunks-by xs by '() '()))
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