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#lang racket
(require advent-of-code
threading
"../../jj-aoc.rkt")
(define input
(~> (fetch-aoc-input (find-session) 2023 14 #:cache #true)
string-split
(map string->list _)
transpose))
(define (roll-boulders board)
(for/list ([col (in-list board)])
(~> col (chunks-by (curry equal? #\#)) (append-map (curryr sort char>?) _))))
(define (score board)
(for*/sum ([col (in-list board)] [(row n) (in-indexed (reverse col))] #:when (equal? row #\O))
(add1 n)))
;; part 1
(~> input roll-boulders score)
;; part 2
(define (rotate-board xss)
(~> xss (map reverse _) transpose))
(define (full-cycle board)
(foldl (λ (_ acc) (~> acc roll-boulders rotate-board)) board (range 4)))
(define (spin-to-win board)
(define cache (make-hash))
(define (do-spin board n)
(match (hash-ref cache board 'not-found)
['not-found
(hash-set! cache board n)
(do-spin (full-cycle board) (sub1 n))]
[seen
(define to-end (modulo n (- seen n)))
(score (foldl (λ (_ acc) (full-cycle acc)) board (range to-end)))]))
(do-spin board 1000000000))
(~> input spin-to-win)
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