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(ql:quickload '(fiveam))
(defparameter eg-vert "#...##..#
#....#..#
..##..###
#####.##.
#####.##.
..##..###
#....#..#")
(defparameter eg-horizontal "#.##..##.
..#.##.#.
##......#
##......#
..#.##.#.
..##..##.
#.#.##.#.")
(defun find-repeat (rows)
(loop for (one two-or-nil) on rows by #'cdr
for idx from 0
when (and (not (null two-or-nil))
(equal one two-or-nil))
collect (1+ idx)))
(defun find-v-mirror (rows)
(remove-if-not (lambda (n) (v-mirror-p rows n))
(find-repeat rows)))
(defun v-mirror-p (rows idx)
(every #'equal
(reverse (subseq rows 0 idx))
(subseq rows idx)))
(defun find-h-mirror (rows)
(find-v-mirror
(transpose-rows rows)))
(defun transpose-rows (rows)
(arrows:-<>
rows
(mapcar #'string-to-octets <>)
(apply #'map 'list (lambda (&rest vals)
(coerce (mapcar #'code-char vals) 'string)) <>)))
(fiveam:test partials
(fiveam:is
(equal '(4)
(find-repeat
(cl-ppcre:split "\\n" eg-vert))))(fiveam:is
(equal '(4)
(find-v-mirror
(cl-ppcre:split "\\n" eg-vert))))
(fiveam:is
(equal '(3)
(find-repeat
(cl-ppcre:split "\\n" eg-horizontal))))
(fiveam:is
(null (find-v-mirror
(cl-ppcre:split "\\n" eg-horizontal))))
(fiveam:is
(equal '(5)
(find-h-mirror
(cl-ppcre:split "\\n" eg-horizontal)))))
(defun solver (maps)
(let ((verical-mirrors (delete nil (mapcan #'find-v-mirror maps)))
(horizontal-mirrors (delete nil (mapcan #'find-h-mirror maps))))
(+
(* 100 (apply #'+ verical-mirrors))
(apply #'+ horizontal-mirrors))))
(defun parse-input (file)
(arrows:->>
(uiop:read-file-string file)
(cl-ppcre:split "\\n\\n")
(mapcar (lambda (map) (cl-ppcre:split "\\n" map)))))
(fiveam:test solutions
(fiveam:is (= 405 (solver (parse-input "eg-in"))))
(fiveam:is (= 35360 (solver (parse-input "input")))))
(fiveam:run!)
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