1 files changed, 49 insertions, 0 deletions
diff --git a/racket/aoc2023/day-14/day-14.rkt b/racket/aoc2023/day-14/day-14.rkt
new file mode 100644
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--- /dev/null
+++ b/racket/aoc2023/day-14/day-14.rkt
@@ -0,0 +1,49 @@
+#lang racket
+
+(require advent-of-code
+         threading
+         "../../jj-aoc.rkt")
+
+(define input
+  (~> (fetch-aoc-input (find-session) 2023 14 #:cache #true)
+      string-split
+      (map string->list _)
+      transpose))
+
+(define (roll-boulders board)
+  (for/list ([col (in-list board)])
+    (~> col (chunks-by (curry equal? #\#)) (append-map (curryr sort char>?) _))))
+
+(define (score board)
+  (for*/sum ([col (in-list board)] 
+             [(row n) (in-indexed (reverse col))] 
+             #:when (equal? row #\O))
+            (add1 n)))
+
+;; part 1
+(~> input 
+    roll-boulders 
+    score)
+
+;; part 2
+(define (rotate-board xss)
+  (~> xss 
+      (map reverse _) 
+      transpose))
+
+(define (full-cycle board)
+  (foldl (λ (_ acc) (~> acc roll-boulders rotate-board)) board (range 4)))
+
+(define (spin-to-win board)
+  (define cache (make-hash))
+  (define (do-spin board n)
+    (match (hash-ref cache board 'not-found)
+      ['not-found
+       (hash-set! cache board n)
+       (do-spin (full-cycle board) (sub1 n))]
+      [seen
+       (define to-end (modulo n (- seen n)))
+       (score (foldl (λ (_ acc) (full-cycle acc)) board (range to-end)))]))
+  (do-spin board 1000000000))
+
+(~> input spin-to-win)