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50 lines
1.7 KiB
Racket
50 lines
1.7 KiB
Racket
4 years ago
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#lang br
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(require racket/file rackunit)
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(define edge-flipped
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(let ()
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(define cache (make-hasheq))
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(define bit-count 10)
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(define (edge-flipper x)
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(for/sum ([(b i)
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(in-indexed (for/list ([b (in-range (sub1 bit-count) -1 -1)])
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(bitwise-bit-set? x b)))]
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#:when b)
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(arithmetic-shift 1 i)))
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(λ (x) (hash-ref cache x (λ () (edge-flipper x))))))
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(struct tile (num edges) #:transparent)
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(define (tilestr->edgevals tilestr)
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(define vec (list->vector (string->list (string-replace tilestr "\n" ""))))
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(for/list ([validxs (list (range 10) ; top
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(range 9 100 10) ; right
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(range 99 89 -1) ; bottom
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(range 90 -1 -10) ; left
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)])
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(for/sum ([idx (in-list validxs)]
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[i (in-naturals)]
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#:when (char=? (vector-ref vec idx) #\#))
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(arithmetic-shift 1 i))))
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(define tiles
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(let* ([recs (string-split (file->string "20.rktd") "Tile")]
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[recs (map string-trim recs)])
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(for/list ([rec recs])
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(match-define (list numstr tilestr) (string-split rec ":"))
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(tile (string->number numstr)
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(tilestr->edgevals tilestr)))))
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(define (matching-edges tile)
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(for/list ([edge (in-list (tile-edges tile))])
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(for/first ([other-tile (in-list (remove tile tiles))]
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#:when
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(for*/or ([other-edge (in-list (tile-edges other-tile))])
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(or (eq? edge other-edge) (eq? edge (edge-flipped other-edge)))))
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other-tile)))
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(define (corner-tile? tile)
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(= 2 (length (filter values (matching-edges tile)))))
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(check-equal? (apply * (map tile-num (filter corner-tile? tiles))) 15405893262491)
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