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(ql:quickload '(fiveam cl-ppcre))
(defparameter eg-input "467..114..
...*......
..35..633.
......#...
617*......
.....+.58.
..592.....
......755.
...$.*....
.664.598..")
(defun inbounds (row-max col-max)
(lambda (cell)
(destructuring-bind (row . col) cell
(and (<= 0 row row-max)
(<= 0 col col-max)))))
(defun contour (row start end)
(list*
(cons row (1- start))
(cons row end)
(loop for i from (1- start) to end
collect (cons (1- row) i)
collect (cons (1+ row) i))))
(defun is-relevant (limits rows)
(lambda(row start end)
(some
(lambda (cell)
(and (funcall limits cell)
(destructuring-bind (row . col) cell
(let ((char (aref (aref rows row) col)))
(not (or (digit-char-p char)
(eq #\. char)))))))
(contour row start end))))
(defun solver1 (lines)
(let* ((rows (make-array (length lines) :initial-contents lines
:adjustable t))
(limits (inbounds (1- (length lines))
(1- (length (car lines)))))
(keep (is-relevant limits rows))
(sum 0))
(loop for row below (length lines)
for content = (aref rows row) do
(cl-ppcre:do-scans (start end _rs _re "\\d+" content)
(when (funcall keep row start end)
;; (format t "~a ~a ~a~%" start end (subseq content start end))
(incf sum (parse-integer (subseq content start end))))))
sum))
(defun adjacent-numbers (line gear-start)
(loop for (num-start num-end) on (cl-ppcre:all-matches "\\d+" line) by #'cddr
when (<= (1- num-start) gear-start num-end)
collect (parse-integer (subseq line num-start num-end))))
(defun solver2 (lines)
(let* ((rows (make-array (length lines) :initial-contents lines
:adjustable t))
(limits (inbounds (1- (length lines))
(1- (length (car lines)))))
(sum 0))
(loop for row below (length lines)
for content = (aref rows row) do
(loop for (gear-start end) on (cl-ppcre:all-matches "\\*" content) by #'cddr do
(let ((ratios
(append
(when (funcall limits (cons (1- row) gear-start))
(adjacent-numbers (aref rows (1- row)) gear-start))
(adjacent-numbers content gear-start)
(when (funcall limits (cons (1+ row) gear-start))
(adjacent-numbers (aref rows (1+ row)) gear-start)))))
(when (= 2 (length ratios))
(incf sum (* (car ratios) (cadr ratios)))))))
sum))
(fiveam:test solutions
(fiveam:is (= 4361 (solver1 (uiop:split-string eg-input :separator '(#\Newline)))))
(fiveam:is (= 467835 (solver2 (uiop:split-string eg-input :separator '(#\Newline)))))
(fiveam:is (= 531561 (solver1 (uiop:read-file-lines "input"))))
(fiveam:is (= 83279367(solver2 (uiop:read-file-lines "input")))))
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