day 18 complete

1 files changed, 57 insertions, 0 deletions

diff --git a/2022/day-18/day-18.rkt b/2022/day-18/day-18.rkt
new file mode 100644
index 0000000..157784d
--- /dev/null
+++ b/2022/day-18/day-18.rkt
@@ -0,0 +1,57 @@
+#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)