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#lang racket
(define LINES (map
(lambda (line)
(let ((command (string-split line)))
(cons
(first command)
(map string->number (rest command)))))
(file->lines "input")))
(define (part-1)
(for/fold ([horizontal 0]
[depth 0]
#:result (* horizontal depth))
([command (in-list LINES)])
(match command
[(list "forward" amount) (values (+ horizontal amount) depth)]
[(list "up" amount) (values horizontal (- depth amount))]
[(list "down" amount) (values horizontal (+ depth amount))]
[_ (error "invalid command")])))
(define (part-2)
(for/fold ([aim 0]
[horizontal 0]
[depth 0]
#:result (* horizontal depth))
([command (in-list LINES)])
(match command
[(list "forward" amount) (values aim (+ horizontal amount) (+ depth (* aim amount)))]
[(list "up" amount) (values (- aim amount) horizontal depth)]
[(list "down" amount) (values (+ aim amount) horizontal depth)]
[_ (error "invalid command")])))
(time
(values
(part-1)
(part-2)))
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