1 files changed, 46 insertions, 0 deletions
diff --git a/racket/aoc2022/day-05/day-05.rkt b/racket/aoc2022/day-05/day-05.rkt
new file mode 100644
index 0000000..76d4ca6
--- /dev/null
+++ b/racket/aoc2022/day-05/day-05.rkt
@@ -0,0 +1,46 @@
+#lang racket
+
+(require advent-of-code
+         threading
+         (only-in relation ->string ->list ->number)
+         (only-in algorithms chunks-of))
+
+(define data (~> (fetch-aoc-input (find-session) 2022 5) (string-split "\n")))
+
+(struct instruction (n from to))
+
+(define crates-list
+  (~>> data
+       (take _ 8)
+       (map (λ~>> ->list))
+       (apply map list _)
+       rest
+       (chunks-of _ 4)
+       (map (λ~> first ->string string-trim ->list) _)))
+
+(define crates
+  (for/hash ([c (in-list crates-list)] [i (in-naturals 1)])
+    (values i c)))
+
+(define (parse-instruction str)
+  (match str
+    [(regexp #px"move (\\d+) from (\\d) to (\\d)" (list _ n from to))
+     (instruction (->number n) (->number from) (->number to))]))
+
+(define instructions (~>> data (drop _ 10) (map parse-instruction)))
+
+(define (find-crate-message cs [reverse-function reverse])
+  (for/fold ([current-crates cs]
+             #:result (~>> (hash-values current-crates) (map first) (apply string)))
+            ([i (in-list instructions)])
+    (match-define (instruction n from to) i)
+    (define taken (~> (hash-ref current-crates from) (take _ n) reverse-function))
+    (~> current-crates
+        (hash-update _ from (λ (v) (drop v n)))
+        (hash-update _ to (λ (v) (append taken v))))))
+
+;; part 1
+(find-crate-message crates)
+
+;; part 2
+(find-crate-message crates identity)