day 15: naive solution

15.rkt

@@ -0,0 +1,41 @@
+#lang curly-fn racket
+
+(require "scripts/aoc.rkt")
+
+;; solution for day 15
+
+(define (naive-solution input limit)
+  (define seen-numbers (make-hash))
+  (define prev #f)
+  (for ([num (in-list input)] [i (in-naturals)])
+    (hash-set! seen-numbers num i)
+    (set! prev num))
+  (hash-remove! seen-numbers prev)
+
+  (for ([i (in-range (length input) limit)])
+    (define new-val
+      (cond
+        [(hash-has-key? seen-numbers prev) (sub1 (- i (hash-ref seen-numbers prev)))]
+        [else 0]))
+    (hash-set! seen-numbers prev (sub1 i))
+    (set! prev new-val))
+  prev)
+
+(define part1 #{naive-solution % 2020})
+(define part2 #{naive-solution % 30000000})
+
+;; parse input file
+(define (parse fname)
+  (define input (string-trim (file->string fname)))
+  (map string->number (string-split input ",")))
+
+(module+ test
+  (require rackunit)
+  ;; tests here
+  (displayln "no tests :("))
+
+(module+ main
+  (define input (parse "inputs/15"))
+  (answer 15 1 (time (part1 input)))
+  (answer 15 2 (time (part2 input)))
+  (displayln "meow"))