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Day 14: Some cleanup.

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Jonathan Chan 2021-12-13 23:05:38 -08:00 committed by Jonathan Chan
parent 80a60ce2f8
commit 08ceca323d
1 changed files with 16 additions and 20 deletions
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36
src/14.rkt
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@ -3,36 +3,32 @@
(require "../lib.rkt") (require "../lib.rkt")
(define-values (template rules left-end right-end) (define-values (template rules left-end right-end)
(match-let ([(list `(,template*) rules) (problem-input-grouped-lines 14)]) (match-let* ([`((,template*) ,rules) (problem-input-grouped-lines 14)]
(define template (map char->symbol (string->list template*))) [(and template `(,left-end ,@_ ,right-end)) (string->list template*)])
(values (for/hash ([left template] (values (for/hash ([left template]
[right (rest template)]) [right (rest template)])
(values (cons left right) 1)) (values (cons left right) 1))
(for/hash ([rule rules]) (for/hash ([rule rules])
(match-let ([(list _ left right insert) (regexp-match #px"(\\w)(\\w) -> (\\w)" rule)]) (match-let ([`(,_ ,left ,right ,insert) (regexp-match #px"(\\w)(\\w) -> (\\w)" rule)])
(values (cons (string->symbol left) (values (cons (string-ref left 0)
(string->symbol right)) (string-ref right 0))
(string->symbol insert)))) (string-ref insert 0))))
(first template) (last template)))) left-end right-end)))
(define (step template) (define (step template)
(for/fold ([polymer (hash)]) (for/fold ([polymer (hash)])
([pair (hash-keys template)]) ([(k v) template])
(match-let* ([(cons left right) pair] (define insert (hash-ref rules k))
[insert (hash-ref rules pair)] (~> polymer
[count (hash-ref template pair)] (hash-update (cons (car k) insert) #{+ % v} 0)
[polymer (hash-update polymer (cons left insert) #{+ % count} 0)] (hash-update (cons insert (cdr k)) #{+ % v} 0))))
[polymer (hash-update polymer (cons insert right) #{+ % count} 0)])
polymer)))
(define (count n) (define (count n)
(for/fold ([counts (hash right-end 1 left-end 1)] (for/fold ([counts (hash right-end 1 left-end 1)]
#:result (let ([counts (hash-values counts)]) #:result (#{/ (- (maximum %) (minimum %)) 2} (hash-values counts)))
(/ (- (maximum counts) (minimum counts)) 2)))
([(k v) ((iterate step n) template)]) ([(k v) ((iterate step n) template)])
(match-let* ([(cons left right) k] (~> counts
[counts (hash-update counts left #{+ % v} 0)] (hash-update (car k) #{+ % v} 0)
[counts (hash-update counts right #{+ % v} 0)]) (hash-update (cdr k) #{+ % v} 0))))
counts)))
(show-solution (count 10) (count 40)) (show-solution (count 10) (count 40))