1 files changed, 82 insertions, 0 deletions
diff --git a/aoc2023-racket/day-07/day-07.rkt b/aoc2023-racket/day-07/day-07.rkt
new file mode 100644
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+++ b/aoc2023-racket/day-07/day-07.rkt
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+#lang racket
+
+(require advent-of-code
+         threading
+         memo)
+
+(struct hand (cards wager))
+
+(define/match (card->int card)
+  [((? char-numeric?)) (~> card string string->number)]
+  [(#\A) 14]
+  [(#\K) 13]
+  [(#\Q) 12]
+  [(#\J) 11]
+  [(#\T) 10]
+  [(#\*) 1])
+
+(define (parse-hand str #:jokers [jokers? #f])
+  (match-define (list card-str wager-str) (string-split str))
+  (define cards
+    (~> card-str
+        ((λ (str) (if jokers? (string-replace str "J" "*") str)))
+        string->list
+        (map card->int _)))
+  (define wager (~> wager-str string->number))
+  (hand cards wager))
+
+(define input (~> (open-aoc-input (find-session) 2023 7 #:cache #true) port->lines))
+
+(define/memoize (identify-hand h)
+  (define freqs (~> h hand-cards (sort <) (group-by identity _) (map length _)))
+  (match freqs
+    [(list-no-order 5) 8]
+    [(list-no-order 1 4) 7]
+    [(list-no-order 2 3) 6]
+    [(list-no-order 1 1 3) 5]
+    [(list-no-order 1 2 2) 4]
+    [(list-no-order 1 1 1 2) 3]
+    [(list-no-order 1 1 1 1 1) 2]
+    [_ 1]))
+
+(define (compare-first-card cs1 cs2)
+  (if (= (first cs1) (first cs2))
+      (compare-first-card (rest cs1) (rest cs2))
+      (< (first cs1) (first cs2))))
+
+(define (compare-hands with h1 h2)
+  (define rank1 (with h1))
+  (define rank2 (with h2))
+  (if (= rank1 rank2) (compare-first-card (hand-cards h1) (hand-cards h2)) (< rank1 rank2)))
+
+;; part 1
+
+(define (compare-hands-no-wilds h1 h2)
+  (compare-hands identify-hand h1 h2))
+
+(define (total-score in #:jokers [jokers? #false])
+  (define sorted-hands
+    (~> in
+        (map (curry parse-hand #:jokers jokers?) _)
+        (sort (if jokers? compare-hands-no-wilds compare-hands-with-wilds))))
+  (for/sum ([(h i)
+             (in-indexed sorted-hands)])
+    (* (add1 i) (hand-wager h))))
+
+(total-score input)
+
+;; part 2
+
+(define/memoize (find-best-joker-substitution h)
+  (for/fold ([best-hand (hand '() 0)]) 
+            ([wild (in-inclusive-range 2 14)])
+    (define trial-hand
+      (hand (map (λ (c) (if (= c 1) wild c)) (hand-cards h)) (hand-wager h)))
+    (if (> (identify-hand trial-hand) (identify-hand best-hand)) 
+        trial-hand 
+        best-hand)))
+
+(define (compare-hands-with-wilds h1 h2)
+  (compare-hands (λ~> find-best-joker-substitution identify-hand) h1 h2))
+
+(total-score input #:jokers #true)