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(defun input-lines (f)
(with-open-file (s f)
(loop for line = (read-line s nil 'eof)
until (eq line 'eof)
collect line)))
(defun split-by-char (char string)
(loop for i = 0 then (1+ j)
as j = (position char string :start i)
collect (subseq string i j)
while j))
(defun parse-integers (string)
(loop for i = 0 then (cadr o)
as o = (multiple-value-list (parse-integer string :start i :junk-allowed t))
as n = (car o)
while n
collect n))
(defun card-winning (winning numbers)
(loop for number in numbers
count (member number winning)))
(defun line-winning (line)
(let ((card-info (split-by-char #\| (cadr (split-by-char #\: line)))))
(let ((winning (parse-integers (car card-info)))
(numbers (parse-integers (cadr card-info))))
(card-winning winning numbers))))
(defun line-points (line)
(ash 1 (1- (line-winning line))))
(defun solve1 (f)
(let ((lines (input-lines f)))
(reduce #'+ (mapcar 'line-points lines))))
(defun solve2 (f)
(let ((lines (input-lines f)))
(let ((arr (make-array (length lines) :initial-element 1)))
(loop for i = 0 then (1+ i)
for line in lines
as count = (line-winning line)
as v = (aref arr i)
do (loop for j from 1 to count
as e = (aref arr (+ i j))
do (setf (aref arr (+ i j)) (+ v e)))
sum v))))
(print (solve1 "data/04/example.txt")) ;; 13
(print (solve1 "data/04/input.txt")) ;; 24160
(print (solve2 "data/04/example.txt")) ;; 30
(print (solve2 "data/04/input.txt")) ;; 5659035
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