22 lines
634 B
Racket
22 lines
634 B
Racket
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#lang curly-fn racket
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(require math/number-theory
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"../lib.rkt")
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(define input (problem-input 13))
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(define timestamp (string->number (first input)))
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(define busses (map string->number (string-split (second input) ",")))
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(define ids (filter identity busses))
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(define part1
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(let* ([waits (map #{- (* % (add1 (quotient timestamp %))) timestamp} ids)]
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[wait (apply min waits)]
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[index (index-of waits wait)])
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(* wait (list-ref ids index))))
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(define part2
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(let ([offsets (filter-map #{and %1 (negate %2)} busses (range (length busses)))])
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(solve-chinese offsets ids)))
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(show-solution part1 part2)
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