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(defun read-lines (filespec)
(with-open-file (stream filespec)
(loop for line = (read-line stream nil)
while line
collect line)))
(defun tilt-map-load (map)
(loop with lstpos = (make-array (length (first map)) :initial-element (1+ (length map)))
for line in map
for i = (length map) then (1- i)
sum (loop for c across line
for j below (length line)
sum (cond ((equal c #\O) (setf (aref lstpos j) (1- (aref lstpos j))))
((equal c #\#) (setf (aref lstpos j) i) 0)
(t 0)))))
(defun solve1 (filespec)
(let ((map (read-lines filespec)))
(tilt-map-load map)))
(defun tilt-west (map)
(loop for line in map
do (loop with nxt = 0
for c across line
for j from 0
when (equal c #\O)
do (progn (when (/= nxt j)
(setf (aref line nxt) #\O
(aref line j) #\.))
(setf nxt (1+ nxt)))
when (equal c #\#)
do (setf nxt (1+ j))))
map)
(defun rotate-clockwise (map)
(let ((map (reverse map)))
(loop for i below (length (first map))
collect (coerce (loop for line in map collect (aref line i)) '(string)))))
(defun rotate-counter-clockwise (map)
(loop for i = (1- (length (first map))) then (1- i)
while (>= i 0)
collect (coerce (loop for line in map collect (aref line i)) '(string))))
(defun map-load (map)
(loop for i = (length map) then (1- i)
for line in map
sum (loop for c across line
when (equal c #\O)
sum i)))
(defun solve2 (filespec &optional (cycles 1000000000))
(let ((map (read-lines filespec))
(tab (make-hash-table :test #'equalp)))
(loop for i below cycles
do (progn (setf map (rotate-counter-clockwise map))
(loop repeat 4
do (setf map (rotate-clockwise (tilt-west map))))
(setf map (rotate-clockwise map)))
until (multiple-value-bind (val found-p) (gethash map tab)
(let ((prev (if found-p val (setf (gethash map tab) i))))
(if (and (> i prev) (= 1 (mod (- cycles i) (- i prev)))) t nil))))
(map-load map)))
(print (solve1 "data/14/example.txt")) ;; 136
(print (solve1 "data/14/input.txt")) ;; 109939
(print (solve2 "data/14/example.txt")) ;; 64
(print (solve2 "data/14/input.txt")) ;; 101010
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