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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))))
(defun flatten-data (data)
(apply #'vector
(mapcan (lambda (row)
(map 'list (lambda (x) (- (char-code x) 48)) row)) data)))
(defun forest (data)
(let ((width (length (car data)))
(height (length data)))
(values (flatten-data data) width height)))
(defun solver-p1 (filename)
(multiple-value-bind (forest-arr width height) (forest (uiop:read-file-lines filename))
(let ((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)
(let ((range (if reverse
(loop for i downfrom (1- minor) to 0 collect i)
(loop for i below minor collect i))))
(dotimes (m major)
(loop
for n in 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))))
(defun solver-p2 (filename)
(multiple-value-bind (forest-arr width height) (forest (uiop:read-file-lines filename))
(let ((score (make-array (* width height)))
(location-x (coord-x-minor width height)))
(flet ((score-direction (base dir)
(loop for l in dir
for tree-height = (aref forest-arr l)
count l until (>= tree-height base))))
(dotimes (y height)
(dotimes (x width)
(let ((base (aref forest-arr (funcall location-x x y))))
(setf (aref score (funcall location-x x y))
(*
(score-direction base (loop for l from (1+ x) below width collect (funcall location-x l y))) ;; to right
(score-direction base (loop for l from (1+ y) below height collect (funcall location-x x l))) ;; to bottom
(score-direction base (loop for l downfrom (1- x) to 0 collect (funcall location-x l y))) ;; to left
(score-direction base (loop for l downfrom (1- y) to 0 collect (funcall location-x x l)))))))) ;; to top
(loop for v across score maximize v)))))
(fiveam:test solutions
(fiveam:is (= 21 (solver-p1 "eg-in")))
(fiveam:is (= 1672 (solver-p1 "input")))
(fiveam:is (= 8 (solver-p2 "eg-in")))
(fiveam:is (= 327180 (solver-p2 "input"))))
(fiveam:run-all-tests)
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