1 files changed, 64 insertions, 0 deletions
diff --git a/racket/aoc2021/day-08/day-08.rkt b/racket/aoc2021/day-08/day-08.rkt
new file mode 100644
index 0000000..6476eae
--- /dev/null
+++ b/racket/aoc2021/day-08/day-08.rkt
@@ -0,0 +1,64 @@
+#lang racket
+(require threading
+         list-utils
+         "../../jj-aoc.rkt")
+
+(struct trial-data (signal output) #:transparent)
+
+(define (string->sets s)
+  (~> s string-split (map (λ~> string->list list->set) _)))
+
+(define data
+  (for/list ([l (in-lines (open-day 8))] #:unless (equal? l ""))
+    (~> l (string-split _ " | ") (map string->sets _) (apply trial-data _))))
+
+;; part 1
+(for*/sum ([trial (in-list data)] [output (in-list (trial-data-output trial))]
+                                  #:when (ormap (λ~> (= (set-count output))) '(2 3 4 7)))
+          1)
+
+;; part 2
+(define (matching-pattern len trial)
+  (define solution-set
+    (for*/list ([signal (in-list (trial-data-signal trial))] #:when (= (set-count signal) len))
+      signal))
+  (match solution-set
+    [(list s) s]
+    [s (apply set-intersect s)]))
+
+(define (determine-arrangement t)
+  (let* ([pattern-1 (matching-pattern 2 t)]
+         [pattern-4 (matching-pattern 4 t)]
+         [pattern-7 (matching-pattern 3 t)]
+         [pattern-8 (matching-pattern 7 t)]
+         [pattern-shared-235 (matching-pattern 5 t)]
+         [pattern-3 (set-union pattern-1 pattern-shared-235)]
+         [pattern-9 (set-union pattern-4 pattern-shared-235)]
+         [pattern-shared-069 (matching-pattern 6 t)]
+         [pattern-just-f (set-subtract pattern-shared-069 pattern-shared-235)]
+         [pattern-just-e
+          (set-subtract pattern-8 (set-union pattern-4 pattern-shared-235 pattern-shared-069))]
+         [pattern-2 (set-union (set-subtract pattern-3 pattern-just-f) pattern-just-e)]
+         [pattern-just-c (set-subtract (set-intersect pattern-4 pattern-7) pattern-just-f)]
+         [pattern-6 (set-subtract pattern-8 pattern-just-c)]
+         [pattern-5 (set-subtract pattern-6 pattern-just-e)]
+         [pattern-0 (set-union (set-subtract pattern-8 pattern-shared-235) pattern-shared-069)])
+    (~> (list pattern-0
+              pattern-1
+              pattern-2
+              pattern-3
+              pattern-4
+              pattern-5
+              pattern-6
+              pattern-7
+              pattern-8
+              pattern-9)
+        enumerate
+        make-hash)))
+
+(for/sum ([trial (in-list data)])
+         (~>> trial
+              trial-data-output
+              (map (λ~>> (hash-ref (determine-arrangement trial))))
+              (apply ~a)
+              string->number))