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day 15: use unsafe for more fast

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xenia 2020-12-15 02:03:03 -05:00
parent 27b79d79ad
commit ef930612d7
1 changed files with 9 additions and 7 deletions
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16
15.rkt
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@ -4,21 +4,23 @@
;; solution for day 15
(require racket/fixnum racket/unsafe/ops)
(define (naive-solution input limit)
(define seen-numbers (make-vector limit #f))
(define seen-numbers (make-fxvector limit -1))
(define prev
(for/last ([num (in-list input)] [i (in-naturals)])
(begin0 num (vector-set! seen-numbers num i))))
(begin0 num (unsafe-fxvector-set! seen-numbers num i))))
;; delay "seeing" numbers by one iteration
(vector-set! seen-numbers prev #f)
(unsafe-fxvector-set! seen-numbers prev -1)
(for/fold ([prev prev]) ([i (in-range (length input) limit)])
(begin0
(match (vector-ref seen-numbers prev)
[#f 0]
[idx (- i 1 idx)])
(match (unsafe-fxvector-ref seen-numbers prev)
[-1 0]
[idx (unsafe-fx- i 1 idx)])
;; _now_ we've "seen" it, but it happened on the last turn
(vector-set! seen-numbers prev (sub1 i)))))
(unsafe-fxvector-set! seen-numbers prev (unsafe-fx- i 1)))))
(define part1 #{naive-solution % 2020})
(define part2 #{naive-solution % 30000000})