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#lang racket
(require "../../jj-aoc.rkt"
threading)
(define coords
(~>> (for/list ([r (in-range 10)])
(for/list ([c (in-range 10)])
(cons r c)))
(apply append)))
(define octopus-data
(~>> (for/list ([l (in-lines (open-day 11 2021))]
#:unless (equal? l ""))
(~>> l
string->list
(map (λ~>> ~a string->number))))
(apply append)
(map cons coords)
make-hash))
(define total-length (hash-count octopus-data))
(define row-length (sqrt total-length))
(define (adjacent-to coord)
(match-define (cons r c) coord)
(for*/list ([row (in-list '(-1 0 1))]
[col (in-list '(-1 0 1))]
#:unless (= 0 row col))
(cons (+ r row) (+ c col))))
(define (simulate-octopi-step data)
(define flashed-this-step (mutable-set))
(let look-for-more-flashes
([octopi (for/hash ([(k v) data])
(values k (add1 v)))]
[flashes-so-far 0])
(define-values (next-octopus-update
flashes-this-update)
(for*/fold ([octopi octopi] [flashes 0])
([(p x) (in-hash octopi)]
#:when (> x 9)
#:unless (set-member? flashed-this-step p))
(set-add! flashed-this-step p)
(define flashed-octopi
(for*/fold ([o (hash-set octopi p 0)])
([adj (in-list (adjacent-to p))]
#:when (hash-has-key? o adj)
#:unless (set-member? flashed-this-step adj))
(hash-update o adj add1)))
(values flashed-octopi
(add1 flashes))))
(if (> flashes-this-update 0)
(look-for-more-flashes next-octopus-update
(+ flashes-so-far
flashes-this-update))
(values next-octopus-update
flashes-so-far))))
;; part 1
(for/fold ([octopi octopus-data]
[total-flashes 0] #:result total-flashes)
([step (in-range 100)])
(define-values [next-state
flashes-from-this-state]
(simulate-octopi-step octopi))
(values next-state
(+ total-flashes flashes-from-this-state)))
;; part 2
(for/fold ([octopi octopus-data]
[synchro-step #f] #:result synchro-step)
([step (in-naturals 1)])
(define-values [next-state
flashes-from-this-state]
(simulate-octopi-step octopi))
#:final (= flashes-from-this-state 100)
(values next-state
step))
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