71 lines
2.0 KiB
Racket
71 lines
2.0 KiB
Racket
#lang curly-fn racket
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(require "../lib.rkt")
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(define input
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(for/vector ([row (problem-input 11)])
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(for/vector ([col (string->list row)])
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(char->number col))))
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(define rows (vector-length input))
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(define cols (vector-length (vector-ref input 0)))
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(define total (* rows cols))
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(define (grid-ref grid row col)
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(vector-ref (vector-ref grid row) col))
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(define (grid-update! grid row col f)
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(let ([vec (vector-ref grid row)])
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(vector-set! vec col (f (vector-ref vec col)))))
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(define (grid-set! grid row col v)
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(grid-update! grid row col (const v)))
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(define (adjs row col)
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(for*/list ([r (range* (max 0 (sub1 row)) (min (sub1 rows) (add1 row)))]
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[c (range* (max 0 (sub1 col)) (min (sub1 cols) (add1 col)))])
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(cons r c)))
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(define (incr! octopodes)
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(for* ([row (range rows)]
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[col (range cols)])
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(grid-update! octopodes row col add1)))
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(define (flash! flashed octopodes)
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(for*/fold ([newly-flashed (set)])
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([row (range rows)]
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[col (range cols)])
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(if (and (not (set-member? flashed (cons row col)))
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(> (grid-ref octopodes row col) 9)
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(for ([adj (adjs row col)])
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(grid-update! octopodes (car adj) (cdr adj) add1)))
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(set-add newly-flashed (cons row col))
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newly-flashed)))
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(define (decharge! octopodes)
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(for* ([row (range rows)]
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[col (range cols)])
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(when (> (grid-ref octopodes row col) 9)
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(grid-set! octopodes row col 0))))
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(define (step! octopodes)
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(incr! octopodes)
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(define flashes
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(let loop ([flashed (set)])
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(let ([newly-flashed (flash! flashed octopodes)])
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(if (set-empty? newly-flashed)
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(set-count flashed)
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(loop (set-union newly-flashed flashed))))))
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(decharge! octopodes)
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flashes)
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(define part1
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(for/sum ([_ (range 100)])
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(step! input)))
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(define part2
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(for/last ([steps (in-naturals 101)]
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#:final (= (step! input) total))
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steps))
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(show-solution part1 part2) |