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#lang racket
(define points (for/set ([line (file->lines "day18")])
(list->vector (map string->number (string-split line ",")))))
(define (neighbors p)
(for/list ([o '(#(-1 0 0)
#( 1 0 0)
#( 0 -1 0)
#( 0 1 0)
#( 0 0 1)
#( 0 0 -1))])
(vector-map + p o)))
(for/sum ([p points])
(for/sum ([n (neighbors p)])
(if (not (set-member? points n))
1
0)))
;; 3550
(define (foldl1 op lst)
(foldl op (car lst) (cdr lst)))
(let ([minx (foldl1 min (map (lambda (v) (vector-ref v 0)) (set->list points)))]
[maxx (foldl1 max (map (lambda (v) (vector-ref v 0)) (set->list points)))]
[miny (foldl1 min (map (lambda (v) (vector-ref v 1)) (set->list points)))]
[maxy (foldl1 max (map (lambda (v) (vector-ref v 1)) (set->list points)))]
[minz (foldl1 min (map (lambda (v) (vector-ref v 2)) (set->list points)))]
[maxz (foldl1 max (map (lambda (v) (vector-ref v 2)) (set->list points)))]
[exterior (mutable-set)])
(define (flood-fill p)
(when (and (<= (- minx 1) (vector-ref p 0) (+ maxx 1))
(<= (- miny 1) (vector-ref p 1) (+ maxy 1))
(<= (- minz 1) (vector-ref p 2) (+ maxz 1))
(not (set-member? points p))
(not (set-member? exterior p)))
(set-add! exterior p)
(for-each flood-fill (neighbors p))))
(flood-fill (vector (- minx 1) (- miny 1) (- minz 1)))
(for/sum ([p points])
(for/sum ([n (neighbors p)])
(if (set-member? exterior n)
1
0))))
;; 2028
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