1 files changed, 51 insertions, 0 deletions
diff --git a/racket/aoc2021/day-04/day-04.rkt b/racket/aoc2021/day-04/day-04.rkt
new file mode 100644
index 0000000..c572f74
--- /dev/null
+++ b/racket/aoc2021/day-04/day-04.rkt
@@ -0,0 +1,51 @@
+#lang racket
+(require advent-of-code
+         threading
+         (only-in algorithms chunks-of))
+
+(define data
+  (for/list ([l (in-lines (open-aoc-input (find-session) 2021 4 #:cache (string->path "./cache")))]
+             #:unless (equal? l ""))
+    l))
+
+(define call-sheet (~> data car (string-split ",") (map string->number _)))
+(define bingo-cards
+  (~> data cdr (map string-split _) (map (λ (row) (map string->number row)) _) (chunks-of 5)))
+
+(define test-card (first bingo-cards))
+
+(define (mark-card card call)
+  (for/list ([row (in-list card)])
+    (for/list ([col (in-list row)])
+      (if (eq? col call) 'X col))))
+
+(define (check-card card)
+  (for/or ([row (in-sequences card (apply map list card))])
+    (equal? row '(X X X X X))))
+
+(define (multiply-by-last-call n call)
+  (match n
+    ['X 0]
+    [n (* n call)]))
+
+(define (evaluate-cards cards calls [check (curry ormap check-card)] [exception not])
+  (for/fold ([current-cards cards]
+             [last-call 0]
+             #:result (~> current-cards
+                          (findf check-card _)
+                          flatten
+                          (map (λ (n) (multiply-by-last-call n last-call)) _)
+                          (apply + _)))
+            ([call (in-list calls)])
+    #:break (check current-cards)
+    (values (for/list ([card (in-list current-cards)] #:unless (exception card))
+              (mark-card card call))
+            call)))
+
+;; part 1
+(evaluate-cards bingo-cards call-sheet)
+;; part 2
+(evaluate-cards bingo-cards
+                call-sheet
+                (λ (cards) (and (= (length cards) 1) (check-card (first cards))))
+                check-card)