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41 lines
1.1 KiB
Racket
41 lines
1.1 KiB
Racket
5 years ago
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#lang debug br
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(require racket/file racket/set)
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(define fp (open-input-file "05.txt"))
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(define fpbs (port->bytes fp))
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(define (react fpbs)
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(let/ec exit
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(for/fold ([bs fpbs])
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([i (in-naturals)])
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(or
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(for/first ([(left lidx) (in-indexed bs)]
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[right (in-bytes (subbytes bs 1))]
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#:when (= 32 (abs (- left right))))
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(bytes-append (subbytes bs 0 lidx) (subbytes bs (+ lidx 2))))
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(exit (bytes-length bs))))))
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(define (★)
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(react fpbs))
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(define possible-units
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(map char->integer (remove-duplicates (map char-upcase (map integer->char (bytes->list fpbs))) char=?)))
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(define (remove-unit fbps unit)
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(apply bytes
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(for/list ([b (in-bytes fbps)]
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#:unless (or (= b unit)
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(= b (+ unit 32))))
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b)))
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;; very slow.
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(define (★★)
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(argmin cdr
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(for/list ([(unit idx) (in-indexed possible-units)])
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(cons unit (react (remove-unit fpbs unit))))))
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(module+ test
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(require rackunit)
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(check-equal? (time (★)) 10564)
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(check-equal? (time (★★)) 6336))
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