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day 15: improve solution spaghettiness somewhat

This commit is contained in:
xenia 2020-12-15 00:27:14 -05:00
parent 4888c7dd40
commit 8b17fe1d26
1 changed files with 11 additions and 10 deletions
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21
15.rkt
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@ -6,20 +6,21 @@
(define (naive-solution input limit) (define (naive-solution input limit)
(define seen-numbers (make-hash)) (define seen-numbers (make-hash))
(define prev #f) (define prev
(for ([num (in-list input)] [i (in-naturals)]) (for/last ([num (in-list input)] [i (in-naturals)])
(hash-set! seen-numbers num i) (hash-set! seen-numbers num i)
(set! prev num)) num))
;; delay "seeing" numbers by one iteration
(hash-remove! seen-numbers prev) (hash-remove! seen-numbers prev)
(for ([i (in-range (length input) limit)]) (for/fold ([prev prev]) ([i (in-range (length input) limit)])
(define new-val (define new-val
(cond (match (hash-ref seen-numbers prev #f)
[(hash-has-key? seen-numbers prev) (sub1 (- i (hash-ref seen-numbers prev)))] [#f 0]
[else 0])) [idx (- i 1 idx)]))
;; _now_ we've "seen" it, but it happened on the last turn
(hash-set! seen-numbers prev (sub1 i)) (hash-set! seen-numbers prev (sub1 i))
(set! prev new-val)) new-val))
prev)
(define part1 #{naive-solution % 2020}) (define part1 #{naive-solution % 2020})
(define part2 #{naive-solution % 30000000}) (define part2 #{naive-solution % 30000000})