diff --git a/21.rkt b/21.rkt
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+++ b/21.rkt
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+#lang curly-fn racket
+
+(require "scripts/aoc.rkt")
+
+;; solution for day 21
+
+(define (part1 input)
+  ; (define edges
+  ;   (for/fold ([edges '()]) ([line (in-list input)])
+  ;     (match-define (cons ingreds allergs) line)
+  ;     (append edges (for*/list ([i (in-list ingreds)] [a (in-list allergs)])
+  ;                     (list i a)))))
+  ; (define G (undirected-graph edges))
+  ;(define matching (maximum-bipartite-matching G))
+  (define all-ingreds (for/fold ([all (set)]) ([line (in-list input)])
+                        (set-union all (list->set (car line)))))
+  (define all-allergs (for/fold ([all (set)]) ([line (in-list input)])
+                        (set-union all (list->set (cdr line)))))
+  (define tainted (mutable-set))
+  (for ([allerg (in-set all-allergs)])
+    (define necessary (for/fold ([necessary all-ingreds]) ([line (in-list input)] #:when (member allerg (cdr line)))
+                        (set-intersect necessary (list->set (car line)))))
+    (set-union! tainted necessary))
+  (define untainted (set-subtract all-ingreds tainted))
+  (for*/sum ([line (in-list input)] [ingred (in-list (car line))])
+    (if (set-member? untainted ingred) 1 0)))
+
+(define (part2 input)
+  (define all-ingreds (for/fold ([all (set)]) ([line (in-list input)])
+                        (set-union all (list->set (car line)))))
+  (define all-allergs (for/fold ([all (set)]) ([line (in-list input)])
+                        (set-union all (list->set (cdr line)))))
+  (define tainted (mutable-set))
+  (for ([allerg (in-set all-allergs)])
+    (define necessary (for/fold ([necessary all-ingreds]) ([line (in-list input)] #:when (member allerg (cdr line)))
+                        (set-intersect necessary (list->set (car line)))))
+    (set-union! tainted necessary))
+
+  (define tainthash (for/hash ([a (in-set all-allergs)])
+                      (values a (for/fold ([is all-ingreds]) ([line (in-list input)] #:when (member a (cdr line)))
+                                  (set-intersect is (list->set (filter #{set-member? tainted %} (car line))))))))
+  (define edges (for*/list ([k (in-list (hash-keys tainthash))]
+                            [v (in-set (hash-ref tainthash k))])
+                  (list k v)))
+
+  (pretty-write edges)
+  (define G (undirected-graph edges))
+  (define matching (maximum-bipartite-matching G))
+  (displayln matching)
+  (define mhash (for/hash ([item (in-list matching)]) (values (first item) (second item))))
+  (displayln mhash)
+  (define by-allergs (sort (hash-keys mhash) string<?))
+  (string-join
+    (for/list ([key (in-list by-allergs)])
+      (hash-ref mhash key))
+    ",")
+
+  )
+
+; (part2 (parse "test"))
+; (error "not shonks")
+
+;; parse input file
+(define (parse fname)
+  (define lines (file->lines fname))
+  (for/list ([line (in-list lines)])
+    (match line
+      [(pregexp #px"^([^\\(]+) \\(contains ([^\\)]+)\\)+"
+                (list _ p1 p2))
+       (define ingredients (string-split p1 " "))
+       (define allergens (string-split p2 ", "))
+       (cons ingredients allergens)]
+      [_ (error "not shonks" line)])))
+
+(module+ test
+  (require rackunit)
+  ;; tests here
+  (displayln "no tests :("))
+
+(module+ main
+  (define input (parse "inputs/21"))
+  (answer 21 1 (time (part1 input)))
+  (answer 21 2 (time (part2 input)))
+  (displayln "meow"))