27 lines
879 B
Racket
27 lines
879 B
Racket
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#lang racket
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(require "../lib.rkt")
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(define input
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(for/list ([line (problem-input 2)])
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(match (string-split line " ")
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[`(,dir ,val) (list (string->symbol dir) (string->number val))])))
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(define part1
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(let ([horiz (sum (filter-map (match-lambda [`(forward ,n) n] [else #f]) input))]
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[ups (sum (filter-map (match-lambda [`(up ,n) n] [else #f]) input))]
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[downs (sum (filter-map (match-lambda [`(down ,n) n] [else #f]) input))])
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(* horiz (- downs ups))))
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(define part2
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(for/fold ([aim 0]
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[horiz 0]
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[depth 0]
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#:result (* horiz depth))
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([dir-val input])
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(match dir-val
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[`(forward ,val) (values aim (+ horiz val) (+ depth (* aim val)))]
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[`(up ,val) (values (- aim val) horiz depth)]
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[`(down ,val) (values (+ aim val) horiz depth)])))
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(show-solution part1 part2)
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