43 lines
1.1 KiB
Racket
43 lines
1.1 KiB
Racket
#lang curly-fn racket
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(require "scripts/aoc.rkt")
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;; solution for day 15
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(define (naive-solution input limit)
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(define seen-numbers (make-hash))
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(define prev
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(for/last ([num (in-list input)] [i (in-naturals)])
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(hash-set! seen-numbers num i)
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num))
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;; delay "seeing" numbers by one iteration
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(hash-remove! seen-numbers prev)
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(for/fold ([prev prev]) ([i (in-range (length input) limit)])
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(define new-val
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(match (hash-ref seen-numbers prev #f)
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[#f 0]
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[idx (- i 1 idx)]))
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;; _now_ we've "seen" it, but it happened on the last turn
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(hash-set! seen-numbers prev (sub1 i))
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new-val))
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(define part1 #{naive-solution % 2020})
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(define part2 #{naive-solution % 30000000})
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;; parse input file
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(define (parse fname)
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(define input (string-trim (file->string fname)))
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(map string->number (string-split input ",")))
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(module+ test
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(require rackunit)
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;; tests here
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(displayln "no tests :("))
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(module+ main
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(define input (parse "inputs/15"))
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(answer 15 1 (time (part1 input)))
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(answer 15 2 (time (part2 input)))
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(displayln "meow"))
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