Advent of Code 2021 https://adventofcode.com/
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#lang racket
(define (tick fishes)
(foldl (λ (fish lst)
(if (= fish 0)
(cons 6 (cons 8 lst))
(cons (sub1 fish) lst))) '() fishes))
(define (generations fishes num)
(if (= num 0)
fishes
(generations (tick fishes) (sub1 num))))
(define part1
(let* ([line (first (file->lines "day6.txt"))]
[fishes (map string->number (string-split line ","))])
(length (generations fishes 80))))
part1
; part2
(define (memo2 fn arg1 arg2)
(let* ([ht (make-hash)])
(hash-ref! ht (list fn arg1 arg2) (fn arg1 arg2))))
(define/match (count-one digit time-left)
[(n 0) 1]
[(0 t) (+ (count-one 6 (sub1 t)) (count-one 8 (sub1 t)))]
[(n t) (count-one (sub1 n) (sub1 t))])
(define count-one-memo (λ (x y) (memo2 count-one x y)))
(define part2-slow
(let* ([line (first (file->lines "day6.txt"))]
[fishes (map string->number (string-split line ","))])
(foldl (λ (x acc) (+ acc (count-one-memo x 100))) 0 fishes)))
; okay so memoing didn't help. ahhh i know what to do
(define (tick2 ht)
(define temp (hash-copy ht))
(hash-set! ht 0 (hash-ref temp 1 0))
(hash-set! ht 1 (hash-ref temp 2 0))
(hash-set! ht 2 (hash-ref temp 3 0))
(hash-set! ht 3 (hash-ref temp 4 0))
(hash-set! ht 4 (hash-ref temp 5 0))
(hash-set! ht 5 (hash-ref temp 6 0))
(hash-set! ht 6 (+ (hash-ref temp 0 0) (hash-ref temp 7 0)))
(hash-set! ht 7 (hash-ref temp 8 0))
(hash-set! ht 8 (hash-ref temp 0 0)))
(define (add-num ht num)
(hash-set! ht num (+ 1 (hash-ref ht num 0))))
(define (init ht nums)
(for ([num (in-list nums)])
(add-num ht num)))
(define (loop ht max)
(if (= 0 max)
ht
(begin
(tick2 ht)
(loop ht (sub1 max)))))
(define part2
(let* ([line (first (file->lines "day6.txt"))]
[fishes (map string->number (string-split line ","))]
[ht (make-hash)])
(begin
(init ht fishes)
(loop ht 256)
(foldl + 0 (hash-values ht)))))
part2