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#lang racket
(require advent-of-code
list-utils
threading
racket/hash)
(define fish-data
(~> (open-aoc-input (find-session) 2021 6 #:cache (string->path "./cache"))
port->string
string-trim
(string-split ",")
(map string->number _)))
(define (simulate-fish time-period)
(for/fold ([state (frequencies fish-data)] #:result (~> state hash-values (apply + _)))
([day (inclusive-range 1 time-period)])
(define day-older-fish
(for/hash ([(days pop) (in-hash state)])
(values (sub1 days) pop)))
(define breeding-fish (hash-ref day-older-fish -1 0))
(hash-union (hash-remove day-older-fish -1) (hash 8 breeding-fish 6 breeding-fish) #:combine +)))
;; part 1
(simulate-fish 80)
;; part 2
(simulate-fish 256)
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