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#lang racket
(require advent-of-code
relation
threading
graph)
(define positions (~> (fetch-aoc-input (find-session) 2022 18 #:cache #true) (string-split "\n")))
(struct posn (x y z) #:transparent)
(define cubes
(for/list ([cube (in-list positions)])
(match (string-split cube ",")
[(list (app ->number x) (app ->number y) (app ->number z)) (posn x y z)])))
(define cubes-set (list->set cubes))
(define (neighbors p)
(match-define (posn x y z) p)
(for*/list ([dx '(-1 0 1)]
[dy '(-1 0 1)]
[dz '(-1 0 1)]
#:when (= 1 (+ (abs dx) (abs dy) (abs dz))))
(posn (+ x dx) (+ y dy) (+ z dz))))
;; part 1
(for*/sum ([cube (in-set cubes-set)]
[neighbor (in-list (neighbors cube))]
#:unless (set-member? cubes-set neighbor))
1)
;; part 2
(define max-x (~> cubes (apply max _ #:key posn-x) posn-x (+ 2)))
(define max-y (~> cubes (apply max _ #:key posn-y) posn-y (+ 2)))
(define max-z (~> cubes (apply max _ #:key posn-z) posn-z (+ 2)))
(define air-set
(for*/set ([x (in-inclusive-range -1 max-x)]
[y (in-inclusive-range -1 max-y)]
[z (in-inclusive-range -1 max-z)]
#:do [(define p (posn x y z))]
#:unless (set-member? cubes-set p))
p))
(define air-graph
(for*/lists (ps #:result (undirected-graph ps))
([a (in-set air-set)]
[neighbor (in-list (neighbors a))]
#:when (set-member? air-set neighbor))
(list a neighbor)))
(for*/sum ([air (in-set (~> air-graph cc (sort > #:key length _) car))]
[neighbor (in-list (neighbors air))]
#:when (set-member? cubes-set neighbor))
1)
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