Refactored Day 5.

src/05.rkt

@@ -1,25 +1,18 @@
 #lang racket
 
-(require "../lib.rkt")
+(require racket/set
+         "../lib.rkt")
 
-(define (string->rc str)
-  (let* ([row-str (substring str 0 7)]
-         [col-str (substring str 7 10)]
-         [as-binary (∘ string->number (∂ string-append "#b"))]
-         [row (as-binary (regexp-replaces row-str '([#rx"F" "0"] [#rx"B" "1"])))]
-         [col (as-binary (regexp-replaces col-str '([#rx"L" "0"] [#rx"R" "1"])))])
-    (cons row col)))
+(define (string->seat str)
+  (string->number (string-append "#b" (regexp-replaces str '([#rx"F" "0"] [#rx"B" "1"] [#rx"L" "0"] [#rx"R" "1"])))))
 
-(define input (map string->rc (problem-input 5)))
+(define input (map string->seat (problem-input 5)))
 
-(define part1
-  (apply max (map (match-lambda [`(,row . ,col) (+ (* row 8) col)]) input)))
-
-(define part2
-  (let ([grid (make-vector-grid 8 128 #\o)])
-    (for ([rc input])
-      (vector-grid-update grid rc #\x))
-    (let ([str (apply string-append (map list->string (vectors->lists grid)))])
-      (add1 (car (first (regexp-match-positions #rx"xox" str)))))))
+(define-values (part1 part2)
+  (let* ([minimum (apply min input)]
+         [maximum (apply max input)]
+         [seats (list->set (range minimum (add1 maximum)))]
+         [filled (list->set input)])
+    (values maximum (set-first (set-subtract seats filled)))))
 
 (show-solution part1 part2)