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54 lines
2.2 KiB
Racket
54 lines
2.2 KiB
Racket
2 years ago
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#lang br
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(require racket/file sugar rackunit racket/dict)
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(define lines (file->lines "14.rktd"))
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(define (template->duos template-str)
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(define cs (string->list template-str))
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(for/list ([c1 cs]
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[c2 (cdr cs)])
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(list c1 c2)))
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(define starting-template (car lines))
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(define template (frequency-hash (template->duos starting-template)))
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(define rule-strs (cddr lines))
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(define procs (for/list ([rule-str rule-strs])
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(match-define (list pat repl) (string-split rule-str " -> "))
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(define duo (string->list pat))
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(define replc (string-ref repl 0))
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(λ (h)
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(match (hash-ref h duo #f)
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[#false null]
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[duo-count
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(define new-left-duo (list (first duo) replc))
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(define new-right-duo (list replc (second duo)))
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(cons
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(cons duo (- duo-count))
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(map (λ (new-duo) (cons new-duo duo-count))
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(list new-left-duo new-right-duo)))]))))
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(define (do-insertion template steps)
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(for/fold ([template template])
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([step steps])
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(define delta-dict (append-map (λ (proc) (proc template)) procs))
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(define this-template (make-hash))
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(for ([(k v) (in-dict (append (hash->list template) delta-dict))])
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(hash-update! this-template k (λ (val) (+ val v)) 0))
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this-template))
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(define (element-counts template)
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(define orig-template-cs (string->list starting-template))
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(define h (make-hash))
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(for* ([(k v) (in-dict template)]
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[c k])
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(hash-update! h c (λ (val) (+ val v)) 0))
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(for-each (λ (c) (hash-update! h c add1)) (list (first orig-template-cs) (last orig-template-cs)))
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(for/hash ([(k v) (in-hash h)])
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(values k (/ v 2))))
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(define (score template)
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(- (apply max (hash-values template)) (apply min (hash-values template))))
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(check-equal? (score (element-counts (do-insertion template 10))) 2703)
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(check-equal? (score (element-counts (do-insertion template 40))) 2984946368465)
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