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(ql:quickload '(fiveam uiop))
(defun coord-x-minor (width height)
(lambda (x y)
(when (and (< -1 x width)
(< -1 y height))
(+ x (* y width)))))
(defun coord-y-minor (width height)
(let ((xminor (coord-x-minor width height)))
(lambda (y x)
(funcall xminor x y))))
(let* ((data (uiop:read-file-lines "input"))
(width (length (car data)))
(height (length data))
(forest-arr
(apply #'vector
(mapcan (lambda (row)
(map 'list (lambda (x) (- (char-code x) 48)) row)) data)))
(visibility-mask (make-array (* width height) :initial-element nil))
(location-x (coord-x-minor width height))
(location-y (coord-y-minor width height))
)
(flet ((toggle-visibility (major minor location reverse)
(dotimes (m major)
(let ((range (loop for i below minor collect i)))
(loop
for n in (if reverse (nreverse range) range)
for maxh = -1 then (max maxh tree-height)
for tree-height = (aref forest-arr (funcall location n m))
when (> tree-height maxh)
do (setf (aref visibility-mask (funcall location n m)) t))))))
(toggle-visibility height width location-x nil)
(toggle-visibility height width location-x t)
(toggle-visibility width height location-y nil)
(toggle-visibility width height location-y t)
)
(loop for v across visibility-mask counting v)
;; visibility-mask
)
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