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day 15: somehow majorly improve speed with begin0

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xenia 2020-12-15 00:37:12 -05:00
parent 8b17fe1d26
commit 8517fd05cc
1 changed files with 5 additions and 7 deletions
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12
15.rkt
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@ -8,19 +8,17 @@
(define seen-numbers (make-hash))
(define prev
(for/last ([num (in-list input)] [i (in-naturals)])
(hash-set! seen-numbers num i)
num))
(begin0 num (hash-set! seen-numbers num i))))
;; delay "seeing" numbers by one iteration
(hash-remove! seen-numbers prev)
(for/fold ([prev prev]) ([i (in-range (length input) limit)])
(define new-val
(begin0
(match (hash-ref seen-numbers prev #f)
[#f 0]
[idx (- i 1 idx)]))
;; _now_ we've "seen" it, but it happened on the last turn
(hash-set! seen-numbers prev (sub1 i))
new-val))
[idx (- i 1 idx)])
;; _now_ we've "seen" it, but it happened on the last turn
(hash-set! seen-numbers prev (sub1 i)))))
(define part1 #{naive-solution % 2020})
(define part2 #{naive-solution % 30000000})