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77 lines
1.9 KiB
Racket
77 lines
1.9 KiB
Racket
3 years ago
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#lang racket
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(define (tick fishes)
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(foldl (λ (fish lst)
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(if (= fish 0)
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(cons 6 (cons 8 lst))
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(cons (sub1 fish) lst))) '() fishes))
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(define (generations fishes num)
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(if (= num 0)
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fishes
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(generations (tick fishes) (sub1 num))))
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(define part1
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(let* ([line (first (file->lines "day6.txt"))]
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[fishes (map string->number (string-split line ","))])
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(length (generations fishes 80))))
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part1
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; part2
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(define (memo2 fn arg1 arg2)
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(let* ([ht (make-hash)])
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(hash-ref! ht (list fn arg1 arg2) (fn arg1 arg2))))
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(define/match (count-one digit time-left)
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[(n 0) 1]
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[(0 t) (+ (count-one 6 (sub1 t)) (count-one 8 (sub1 t)))]
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[(n t) (count-one (sub1 n) (sub1 t))])
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(define count-one-memo (λ (x y) (memo2 count-one x y)))
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(define part2-slow
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(let* ([line (first (file->lines "day6.txt"))]
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[fishes (map string->number (string-split line ","))])
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(foldl (λ (x acc) (+ acc (count-one-memo x 100))) 0 fishes)))
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; okay so memoing didn't help. ahhh i know what to do
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(define (tick2 ht)
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(define temp (hash-copy ht))
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(hash-set! ht 0 (hash-ref temp 1 0))
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(hash-set! ht 1 (hash-ref temp 2 0))
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(hash-set! ht 2 (hash-ref temp 3 0))
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(hash-set! ht 3 (hash-ref temp 4 0))
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(hash-set! ht 4 (hash-ref temp 5 0))
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(hash-set! ht 5 (hash-ref temp 6 0))
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(hash-set! ht 6 (+ (hash-ref temp 0 0) (hash-ref temp 7 0)))
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(hash-set! ht 7 (hash-ref temp 8 0))
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(hash-set! ht 8 (hash-ref temp 0 0)))
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(define (add-num ht num)
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(hash-set! ht num (+ 1 (hash-ref ht num 0))))
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(define (init ht nums)
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(for ([num (in-list nums)])
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(add-num ht num)))
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(define (loop ht max)
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(if (= 0 max)
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ht
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(begin
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(tick2 ht)
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(loop ht (sub1 max)))))
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(define part2
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(let* ([line (first (file->lines "day6.txt"))]
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[fishes (map string->number (string-split line ","))]
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[ht (make-hash)])
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(begin
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(init ht fishes)
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(loop ht 256)
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(foldl + 0 (hash-values ht)))))
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part2
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