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#lang racket
(require advent-of-code)
(define raw-packets
(parameterize ([current-readtable (make-readtable #f #\, #\space #f)])
(port->list read (open-aoc-input (find-session) 2022 13 #:cache #true))))
(define (compare xs ys)
(match* (xs ys)
[('() (list* _)) #true]
[((list* _) '()) #false]
[((list* _same x-rest) (list* _same y-rest)) (compare x-rest y-rest)]
[((list* (? integer? x) _) (list* (? integer? y) _)) (< x y)]
[((list* (? list? xs*) _) (list* (? list? ys*) _)) (compare xs* ys*)]
[(xs (list* (? integer? y) y-rest)) (compare xs (cons (list y) y-rest))]
[((list* (? integer? x) x-rest) ys) (compare (cons (list x) x-rest) ys)]))
;; part 1
(for/sum ([i (in-naturals 1)] [packet (in-slice 2 raw-packets)] #:when (apply compare packet)) i)
;; part 2
(define divider-packets (list '((2)) '((6))))
(define amended-packets (append divider-packets raw-packets))
(for/product ([i (in-naturals 1)] [packet (in-list (sort amended-packets compare))]
#:when (member packet divider-packets))
i)
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