day 24: u___u

24.rkt

@@ -0,0 +1,80 @@
+#lang curly-fn racket
+
+(require "scripts/aoc.rkt")
+
+;; solution for day 24
+
+; (define d->r degrees->radians)
+; (define (i->e x) (inexact->exact (round x)))
+(struct hex [x y z] #:transparent)
+(define (hex+ a b)
+  (hex (+ (hex-x a) (hex-x b))
+       (+ (hex-y a) (hex-y b))
+       (+ (hex-z a) (hex-z b))))
+
+(define *dirs* (hash
+                 'e (hex 1 -1 0)
+                 'ne (hex 1 0 -1)
+                 'nw (hex 0 1 -1)
+                 'w (hex -1 1 0)
+                 'sw (hex -1 0 1)
+                 'se (hex 0 -1 1)))
+
+(define (paths->tiles input)
+  (define tiles (make-hash))
+  (for ([path (in-list input)])
+    (define posn
+      (for/fold ([posn (hex 0 0 0)]) ([p (in-list path)])
+        (hex+ posn (hash-ref *dirs* p))))
+    (hash-update! tiles posn not #f))
+  tiles)
+
+(define (part1 input)
+  ;; white is #f
+  ;; black is #t
+  (define tiles (paths->tiles input))
+  (for/sum ([(_ v) (in-hash tiles)] #:when v) 1))
+
+(define (part2 input)
+  (define tiles (paths->tiles input))
+
+  (define (step tiles)
+    (define new-tiles (make-hash))
+    (define minx (apply min (map hex-x (hash-keys tiles))))
+    (define maxx (apply max (map hex-x (hash-keys tiles))))
+    (define miny (apply min (map hex-y (hash-keys tiles))))
+    (define maxy (apply max (map hex-y (hash-keys tiles))))
+    (define minz (apply min (map hex-z (hash-keys tiles))))
+    (define maxz (apply max (map hex-z (hash-keys tiles))))
+    (for* ([x (in-range (sub1 minx) (+ maxx 2))] [y (in-range (sub1 miny) (+ maxy 2))] [z (in-range (sub1 minz) (+ maxz 2))] #:when (zero? (+ x y z)))
+      (define thispos (hex x y z))
+      (define thistile (hash-ref tiles thispos #f))
+      (define num-blacks (for/sum ([t (in-list (hash-values *dirs*))] #:when (hash-ref tiles (hex+ thispos t) #f)) 1))
+      (hash-set! new-tiles thispos
+                 (cond
+                   [(and thistile (or (zero? num-blacks) (> num-blacks 2))) #f]
+                   [thistile #t]
+                   [(= num-blacks 2) #t]
+                   [else #f])))
+    new-tiles)
+
+  (define end (for/fold ([tiles tiles]) ([i (in-range 100)]) (displayln i) (step tiles)))
+
+  (for/sum ([(_ v) (in-hash end)] #:when v) 1))
+
+;; parse input file
+(define (parse fname)
+  (for/list ([line (in-list (file->lines fname))])
+    (map string->symbol (regexp-match* #px"(e|se|sw|w|nw|ne)" line))))
+
+
+(module+ test
+  (require rackunit)
+  ;; tests here
+  (displayln "no tests :("))
+
+(module+ main
+  (define input (parse "inputs/24"))
+  (answer 24 1 (time (part1 input)))
+  (answer 24 2 (time (part2 input)))
+  (displayln "meow"))