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;; 6:34
;; 8:11 part 1
;; 9:36 part 2
(ql:quickload '(fiveam arrows cl-ppcre))
(defparameter eg-vert "#...##..#
#....#..#
..##..###
#####.##.
#####.##.
..##..###
#....#..#")
(defparameter eg-horizontal "#.##..##.
..#.##.#.
##......#
##......#
..#.##.#.
..##..##.
#.#.##.#.")
(defun count-differences (a b)
(loop for x across a
for y across (or b "")
count (not (eq x y))))
(defun v-mirror (rows &optional (max-differences 0))
(loop
for idx from 1 below (length rows)
when
(= max-differences
(loop
for above in (reverse (subseq rows 0 idx))
for below in (subseq rows idx)
sum (count-differences above below)))
do (return idx)))
(defun h-mirror (rows &optional (max-differences 0))
(v-mirror (transpose-rows rows) max-differences))
(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
(= 4
(v-mirror
(cl-ppcre:split "\\n" eg-vert))))
(fiveam:is
(= 1
(v-mirror
(cl-ppcre:split "\\n" eg-vert) 1)))
(fiveam:is
(null (v-mirror
(cl-ppcre:split "\\n" eg-horizontal))))
(fiveam:is
(= 3 (v-mirror
(cl-ppcre:split "\\n" eg-horizontal) 1)))
(fiveam:is
(= 5
(h-mirror
(cl-ppcre:split "\\n" eg-horizontal))))
(fiveam:is
(null (h-mirror
(cl-ppcre:split "\\n" eg-horizontal) 1))))
(defun solver (maps &optional (max-differences 0))
(let ((vertical-mirrors (delete nil (mapcar (lambda (m)
(v-mirror m max-differences))
maps)))
(horizontal-mirrors (delete nil (mapcar (lambda (m)
(h-mirror m max-differences))
maps))))
(+
(* 100 (apply #'+ vertical-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 (= 400 (solver (parse-input "eg-in") 1)))
(fiveam:is (= 35360 (solver (parse-input "input"))))
(fiveam:is (= 36755 (solver (parse-input "input") 1))))
(fiveam:run!)
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