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day 15: switch to vector for more good perf

This commit is contained in:
xenia 2020-12-15 01:16:04 -05:00
parent 8517fd05cc
commit 27b79d79ad
1 changed files with 5 additions and 5 deletions
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10
15.rkt
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@ -5,20 +5,20 @@
;; solution for day 15
(define (naive-solution input limit)
(define seen-numbers (make-hash))
(define seen-numbers (make-vector limit #f))
(define prev
(for/last ([num (in-list input)] [i (in-naturals)])
(begin0 num (hash-set! seen-numbers num i))))
(begin0 num (vector-set! seen-numbers num i))))
;; delay "seeing" numbers by one iteration
(hash-remove! seen-numbers prev)
(vector-set! seen-numbers prev #f)
(for/fold ([prev prev]) ([i (in-range (length input) limit)])
(begin0
(match (hash-ref seen-numbers prev #f)
(match (vector-ref seen-numbers prev)
[#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)))))
(vector-set! seen-numbers prev (sub1 i)))))
(define part1 #{naive-solution % 2020})
(define part2 #{naive-solution % 30000000})