Day 21. I'll refactor later lmao

src/21.rkt

@@ -0,0 +1,71 @@
+#lang curly-fn racket
+
+(require "../lib.rkt")
+
+(define-values (p1 p2) (values 1 6))
+
+(define (% n m)
+  (if (zero? (modulo n m)) m (modulo n m)))
+
+(define (inc roll)
+  (+ (% (+ roll 0) 100)
+     (% (+ roll 1) 100)
+     (% (+ roll 2) 100)))
+
+(define part1
+  (let loop ([roll 1]
+             [rolls 0]
+             [next (cons p1 0)]
+             [prev (cons p2 0)])
+    (define pos*
+      (% (+ (car next) (inc roll)) 10))
+    (define score*
+      (+ (cdr next) pos*))
+    (if (>= score* 1000)
+        (* (cdr prev) (+ rolls 3))
+        (loop (% (+ roll 3) 100) (+ rolls 3)
+              prev (cons pos* score*)))))
+
+(define rolls
+  (hash 3 1
+        4 3
+        5 6
+        6 7
+        7 6
+        8 3
+        9 1))
+
+(define part2
+  (let loop ([univs (hash (list p1 0 p2 0) 1)]
+             [wins1 0]
+             [wins2 0])
+    (cond
+      [(hash-empty? univs) (max wins1 wins2)]
+      [else
+       (define-values (univs* wins1*)
+         (for*/fold ([univs (hash)]
+                     [wins wins1])
+                    ([(pp u) univs]
+                     [(r m) rolls])
+           (match-define (list p1 s1 p2 s2) pp)
+           (define p1* (% (+ p1 r) 10))
+           (define s1* (+ s1 p1*))
+           (define u* (* u m))
+           (if (>= s1* 21)
+               (values univs (+ wins u*))
+               (values (hash-update univs (list p1* s1* p2 s2) #{+ % u*} 0) wins))))
+       (define-values (univs** wins2*)
+         (for*/fold ([univs (hash)]
+                     [wins wins2])
+                    ([(pp u) univs*]
+                     [(r m) rolls])
+           (match-define (list p1 s1 p2 s2) pp)
+           (define p2* (% (+ p2 r) 10))
+           (define s2* (+ s2 p2*))
+           (define u* (* u m))
+           (if (>= s2* 21)
+               (values univs (+ wins u*))
+               (values (hash-update univs (list p1 s1 p2* s2*) #{+ % u*} 0) wins))))
+       (loop univs** wins1* wins2*)])))
+
+(show-solution part1 part2)