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#lang racket
(define area (build-vector 800 (lambda _ (make-vector 800 0))))
(define (area-get x y)
(vector-ref (vector-ref area y) x))
(define (area-set! x y v)
(vector-set! (vector-ref area y) x v))
(define/match (draw from to)
[((list x y1) (list x y2))
(for ([y (in-inclusive-range (min y1 y2) (max y1 y2))])
(area-set! x y 9))]
[((list x1 y) (list x2 y))
(for ([x (in-inclusive-range (min x1 x2) (max x1 x2))])
(area-set! x y 9))])
(for ([line (file->lines "day14")])
(let ([coords (for/list ([coord (string-split line " -> ")])
(map string->number (string-split coord ",")))])
(for ([from coords]
[to (cdr coords)])
(draw from to))))
(define (drop-sand x y)
(if (or (>= y 799) (>= x 799))
#f
(case (area-get x (+ y 1))
[(0) (drop-sand x (+ y 1))]
[(1 9) (case (area-get (- x 1) (+ y 1))
[(0) (drop-sand (- x 1) (+ y 1))]
[(1 9) (case (area-get (+ x 1) (+ y 1))
[(0) (drop-sand (+ x 1) (+ y 1))]
[(1 9) (area-set! x y 1)])])])))
(let loop ([i 0])
(if (drop-sand 500 0)
(loop (+ 1 i))
i))
;; 665
;; clear sand
(void
(vector-map! (lambda (line) (vector-map! (lambda (x) (if (= x 1) 0 x)) line)) area))
(void
(for/and ([i (in-inclusive-range 599 0 -1)])
(when (for/or ([item (vector-ref area i)])
(= item 9))
(draw (list 0 (+ i 2))
(list 799 (+ i 2)))
#f)))
(let loop ([i 0])
(if (= (area-get 500 0) 1)
i
(begin
(drop-sand 500 0)
(loop (+ 1 i)))))
;; 25434
;; (for ([line area]) (displayln line))
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