5 files changed, 136 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)))
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)))
diff --git a/2021/day4/04t.rkt b/2021/day4/04t.rkt
new file mode 100644
index 0000000..b3f10ad
--- /dev/null
+++ b/2021/day4/04t.rkt
@@ -0,0 +1,9 @@
+#lang reader "reader.rkt"
+7,4,9,5,11,17,23,2,0,14,21,24,10,16,13,6,15,25,12,22,18,20,8,19,3,26,1
+
+22 13 17 11  0
+ 8  2 23  4 24
+21  9 14 16  7
+ 6 10  3 18  5
+1 12 20 15 19
+
diff --git a/2021/day4/parser.rkt b/2021/day4/parser.rkt
new file mode 100644
index 0000000..449d886
--- /dev/null
+++ b/2021/day4/parser.rkt
@@ -0,0 +1,8 @@
+#lang brag
+file: numbers "\n" "\n" boards
+numbers: number ("," number)*
+number: digit+
+digit: "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"
+boards: board ("\n" board)*
+board: row "\n" row "\n" row "\n" row "\n" row "\n"
+row: " "+ number " "+ number " "+ number " "+ number " "+ number
diff --git a/2021/day4/reader.rkt b/2021/day4/reader.rkt
new file mode 100644
index 0000000..b777f92
--- /dev/null
+++ b/2021/day4/reader.rkt
@@ -0,0 +1,21 @@
+#lang racket
+
+(require "parser.rkt")
+(require brag/support)
+
+(define (make-tokenizer port)
+  (define (next-token)
+    (define bf-lexer
+      (lexer
+       [(char-set "\n1234567890, ") lexeme]
+       [any-char (next-token)]))
+    (bf-lexer port))
+  next-token)
+
+(define (read-syntax path port)
+  (define parse-tree (parse path (make-tokenizer port)))
+  (define module-datum `(module day4 racket
+                          ,parse-tree))
+  (datum->syntax #f module-datum))
+
+(provide read-syntax)