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#lang racket
(require advent-of-code
threading
algorithms)
(define motion-data
(~> (open-aoc-input (find-session) 2021 2 #:cache (string->path "./cache"))
(port->list read _)
(chunks-of _ 2)))
;; part 1
(for/fold ([depth 0] [position 0] #:result (* depth position)) ([motion (in-list motion-data)])
(match motion
[(list 'forward x) (values depth (+ position x))]
[(list 'up x) (values (- depth x) position)]
[(list 'down x) (values (+ depth x) position)]))
;; part 2
(for/fold ([aim 0] [depth 0] [position 0] #:result (* depth position))
([motion (in-list motion-data)])
(match motion
[(list 'forward x) (values aim (+ depth (* aim x)) (+ position x))]
[(list 'up x) (values (- aim x) depth position)]
[(list 'down x) (values (+ aim x) depth position)]))
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