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#lang racket
(require advent-of-code
threading
rebellion/collection/entry
rebellion/collection/multidict)
(define raw-rules (~> (open-aoc-input (find-session) 2020 7) (port->string) (string-split "\n")))
(define (split-rule r)
(match-define (list head tail) (string-split (string-trim r #px" bags?.") " bags contain "))
(~>> tail
(regexp-split #px"( bags?,\\s)" _)
(map (λ~> (regexp-match* #px"(\\d+) (\\w+ \\w+)" _ #:match-select rest)))
append*
(map (λ~> (match _
[(list n c) (list (string->symbol c) (string->number n))]
['() '()])))
(cons (string->symbol head) _)))
(define rules-multidict
(for*/multidict ([ln (in-list raw-rules)] #:do [(match-define (list* from tos) (split-rule ln))]
[to (in-list tos)])
(entry from to)))
;; part 1
(define (bags-that-eventually-contain target)
(for/fold ([holders (set)]) ([rule (in-multidict-entries rules-multidict)])
(match rule
[(entry outside (list (== target) _))
(set-union (set-add holders outside) (bags-that-eventually-contain outside))]
[_ holders])))
(define part-1 (set-count (bags-that-eventually-contain '|shiny gold|)))
(~a "Part 1: " part-1)
;; (aoc-submit (find-session) 2020 7 1 part-1)
;; part 2
(define (bags-that-are-contained-by target)
(for/sum ([holding (in-multidict-entries rules-multidict)])
(match holding
[(entry (== target) (list held n)) (+ n (* n (bags-that-are-contained-by held)))]
[_ 0])))
(define part-2 (bags-that-are-contained-by '|shiny gold|))
(~a "Part 2: " part-2)
;; (aoc-submit (find-session) 2020 7 1 part-2)
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