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#lang racket
(require "../../jj-aoc.rkt"
threading
racket/hash)
(struct pixel (i j) #:transparent)
(define-values (raw-enhancement raw-image)
(~> (open-day 20 2021)
port->string
(string-split "\n\n")
(apply values _)))
(define (char->pixel c) (if (char=? #\# c) 'light 'dark))
(define (pixel->char c) (if (equal? 'light c) #\# #\.))
(define enhancement-algorithm
(for/hash ([(c i) (in-indexed (~> raw-enhancement (string-replace "\n" "")))])
(values i (char->pixel c))))
(define image-hash
(for*/hash ([(row i) (in-indexed (string-split raw-image "\n"))]
[(c j) (in-indexed row)])
(values (pixel i j) (char->pixel c))))
(define (window->new-pixel p ps bg)
(match-define (pixel i j) p)
(~> (for*/list ([di '(-1 0 1)]
[dj '(-1 0 1)])
(if (equal? 'dark (hash-ref ps (pixel (+ i di) (+ j dj)) bg)) #\0 #\1))
(apply string _)
(string->number _ 2)
(hash-ref enhancement-algorithm _)))
(define (pad-hash ps bg)
(define coords (hash-keys ps))
(define i-min (~>> coords (map pixel-i) (apply min)))
(define i-max (~>> coords (map pixel-i) (apply max)))
(define j-min (~>> coords (map pixel-j) (apply min)))
(define j-max (~>> coords (map pixel-j) (apply max)))
(for*/hash ([i (in-inclusive-range (- i-min 2) (+ i-max 2))]
[j (in-inclusive-range (- j-min 2) (+ j-max 2))])
(values (pixel i j) (hash-ref ps (pixel i j) bg))))
(define (enhance-image ps bg)
(for/hash ([(p _) (in-hash (pad-hash ps bg))])
(values p (window->new-pixel p ps bg))))
;; part 1
;; looking at the enhancement algorithm, since a window of 0 -> light and 512 -> dark,
;; the infinite background flips colors every other enhancement step
;; instead of trying to account for this algorithmically I just hardcoded it in
(~> image-hash
(enhance-image 'dark)
(enhance-image 'light)
hash-values
(count (curry equal? 'light) _))
;; part 2
(~> (for/fold ([img image-hash])
([_ (in-range 25)])
(~> img
(enhance-image 'dark)
(enhance-image 'light)))
hash-values
(count (curry equal? 'light) _))
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