day 3: less spaghet

3.rkt

@@ -4,33 +4,27 @@
 
 ;; solution for day 3
 
-(define prios (string->list "_abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"))
+(define priorities
+  (string->list "_abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"))
 
 (define (part1 input)
   (for/sum ([line (in-list input)])
-    (define len (string-length line))
-    (define h1 (substring line 0 (/ len 2)))
-    (define h2 (substring line (/ len 2) len))
-    (define g1 (list->set (string->list h1)))
-    (define g2 (list->set (string->list h2)))
-    (define both (set-intersect g1 g2))
-    (index-of prios (first (set->list both)))))
-
+    (define-values [left right] (split-at line (/ (length line) 2)))
+    (~>> (set-intersect left right)
+         (set-first)
+         (index-of priorities))))
 
 (define (part2 input)
-  (displayln (length input))
-  (for/sum ([i (in-range 0 (length input) 3)])
-    (define l1 (list-ref input (+ i 0)))
-    (define l2 (list-ref input (+ i 1)))
-    (define l3 (list-ref input (+ i 2)))
-    (define g1 (list->set (string->list l1)))
-    (define g2 (list->set (string->list l2)))
-    (define g3 (list->set (string->list l3)))
-    (define both (set-intersect (set-intersect g1 g2 ) g3))
-    (index-of prios (first (set->list both)))))
+  (match input
+    ['() 0]
+    [(list* a b c rst)
+     (+ (~>> (set-intersect a b c)
+             (set-first)
+             (index-of priorities))
+        (part2 rst))]))
 
 (define (parse fname)
-  (file->lines fname))
+  (map string->list (file->lines fname)))
 
 (module+ main
   (define input (parse "inputs/3"))