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@ -73,3 +73,45 @@
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(let ((data (read-2 file)))
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(time (progn (print (%solve-2 data #'%solve-2-1))
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(print (%solve-2 data #'%solve-2-2))))))
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(defun read-3 (file)
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(with-open-file (stream file)
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(let ((temp-map (loop for line = (read-line stream nil)
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while line
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collect line)))
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(make-array (list (length temp-map) (length (first temp-map)))
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:initial-contents temp-map
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:element-type 'character))))
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(defun step-slope (position direction map)
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(let* ((temp-position (map 'list #'+ direction position))
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(overflow (map 'list #'> temp-position (array-dimensions map))))
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(cond ((first overflow) :bottom)
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((second overflow)
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(progn (decf (second temp-position) (second (array-dimensions map)))
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temp-position))
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(t temp-position))))
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(defun solve-3-1 (direction map)
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(let ((tree-count 0))
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(labels ((rec (position)
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(let ((zero-pos (map 'list #'1- position))
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(new-pos (step-slope position direction map)))
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(if (char= (aref map (first zero-pos) (second zero-pos))
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#\#)
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(incf tree-count))
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(unless (eq new-pos :bottom)
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(rec new-pos)))))
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(rec '(1 1))
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tree-count)))
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;; (height width)
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(defun solve-3-2 (slopes map)
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(reduce #'* (loop for slope in slopes
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collecting (solve-3-1 slope map))))
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(defun solve-3 (map)
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(time (let ((data (read-3 map)))
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(print (solve-3-1 '(1 3) data))
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(print (solve-3-2 '((1 1) (1 3) (1 5) (1 7) (2 1)) data)))))
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