Day 03.

src/03.rkt

@@ -0,0 +1,36 @@
+#lang curly-fn racket
+
+(require "../lib.rkt")
+
+(define input
+  (for/list ([b (problem-input 3)])
+    (string->list b)))
+
+(define chars->binary
+  (∘ string->binary list->string))
+
+(define (nth-bit nums p n)
+  (let ([bs (map #{list-ref % n} nums)])
+    (if (p (count (∂ char=? #\1) bs) (/ (length nums) 2))
+        #\1 #\0)))
+
+(define (squimsh p)
+  (~> (range (length (first input)))
+      (map #{nth-bit input p %} _)
+      chars->binary))
+
+(define (search p)
+  (let loop ([nums input]
+             [n 0])
+    (if (= (length nums) 1)
+        (chars->binary (first nums))
+        (let ([bit (nth-bit nums p n)])
+          (loop (filter #{char=? bit (list-ref % n)} nums) (add1 n))))))
+
+(define part1
+  (* (squimsh >=) (squimsh <)))
+
+(define part2
+  (* (search >=) (search <)))
+
+(show-solution part1 part2)