1 files changed, 49 insertions, 0 deletions
diff --git a/2021/day4/04a-alt.rkt b/2021/day4/04a-alt.rkt
new file mode 100644
index 0000000..db03881
--- /dev/null
+++ b/2021/day4/04a-alt.rkt
@@ -0,0 +1,49 @@
+#lang racket
+
+(require racket/file)
+
+(define (parse-row x)
+  (map string->number (filter (lambda (x) (< 0 (string-length x))) (regexp-split #rx" +" x))))
+
+(define (parse-board x)
+  (map parse-row (string-split x "\n")))
+
+(define (get-numbers x)
+  (define number-line (car (string-split x "\n\n")))
+  (map string->number (string-split number-line ",")))
+
+(define (get-boards x)
+  (define boards (cdr (string-split x "\n\n")))
+  (map parse-board boards))
+
+(define (subsetOf xs ys)
+  (subset? (list->set xs) (list->set ys)))
+
+(define (transpose xs)
+  (apply map list xs))
+
+(define (check-win board numbers)
+  (define winningColumns (filter (lambda (x) (subsetOf x numbers)) board))
+  (define winningRows (filter (lambda (x) (subsetOf x numbers)) (transpose board)))
+  (cond [(not (null? winningColumns)) (car winningColumns)]
+        [(not (null? winningRows)) (car winningRows)]
+        [else #f]))
+
+(define input (file->string "./input"))
+(define numbers (get-numbers input))
+(define boards (get-boards input))
+
+(define winningBoard #f)
+(define winningRun #f)
+(define wonOnRound 0)
+(for* ([rnd (length numbers)]
+       [board boards]
+       #:unless winningRun
+       )
+  (set! winningRun (check-win board (take numbers rnd)))
+  (set! winningBoard board)
+  (set! wonOnRound rnd))
+
+(*
+ (foldr + 0 (filter (lambda (x) (not (member x (take numbers wonOnRound)))) (flatten winningBoard)))
+ (list-ref numbers (- wonOnRound 1)))