1 files changed, 49 insertions, 0 deletions
diff --git a/2021/day4/04b-alt.rkt b/2021/day4/04b-alt.rkt
new file mode 100644
index 0000000..ab32bc2
--- /dev/null
+++ b/2021/day4/04b-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 ht (make-hash))
+(for* ([rnd (length numbers)]
+       [board boards]
+       #:unless (hash-ref ht board #f)
+       )
+  (cond [(check-win board (take numbers rnd)) (hash-set! ht board rnd)]))
+
+(define maxTurn 0)
+(define lastBoard #f)
+(hash-for-each ht (lambda (k v) (cond [(> v maxTurn) (set! maxTurn v) (set! lastBoard k)])))
+
+(*
+ (foldr + 0 (filter (lambda (x) (not (member x (take numbers maxTurn)))) (flatten lastBoard)))
+ (list-ref numbers (- maxTurn 1)))