50 lines
1.5 KiB
Racket
50 lines
1.5 KiB
Racket
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#lang curly-fn racket
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(require "../lib.rkt"
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data/queue)
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(define droplets
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(~>> (problem-input 18)
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(map #{string-split % ","})
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(mmap string->number)
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(apply set)))
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(define xmax (for/max ([droplet droplets]) (first droplet)))
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(define ymax (for/max ([droplet droplets]) (second droplet)))
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(define zmax (for/max ([droplet droplets]) (third droplet)))
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(define (neighbours x y z)
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(filter #{match-let ([`(,x ,y ,z) %])
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(and (<= -1 x (add1 xmax))
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(<= -1 y (add1 ymax))
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(<= -1 z (add1 zmax)))}
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`((,(add1 x) ,y ,z)
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(,(sub1 x) ,y ,z)
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(,x ,(add1 y) ,z)
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(,x ,(sub1 y) ,z)
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(,x ,y ,(add1 z))
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(,x ,y ,(sub1 z)))))
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(define outside
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(let ([Q (make-queue)])
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(enqueue! Q '(-1 -1 -1))
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(let loop ([outside (set '(-1 -1 -1))])
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(if (queue-empty? Q)
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outside
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(for/fold ([outside outside]
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#:result (loop outside))
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([neighbour (apply neighbours (dequeue! Q))]
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#:when (not (or (set-member? outside neighbour)
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(set-member? droplets neighbour))))
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(enqueue! Q neighbour)
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(set-add outside neighbour))))))
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(define part1
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(for/sum ([droplet droplets])
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(length (filter #{not (set-member? droplets %)} (apply neighbours droplet)))))
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(define part2
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(for/sum ([droplet droplets])
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(length (filter #{set-member? outside %} (apply neighbours droplet)))))
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(show-solution part1 part2)
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