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(in-package :aoc/2024)
(defparameter *input/d1*
(asdf:system-relative-pathname :advent "2024/d01.input"))
(defun readlists (filename)
"Read the left and right columns of numbers into individual lists"
(let ((left-numbers '())
(right-numbers '()))
(with-open-file (stream filename :direction :input)
(loop for line = (read-line stream nil nil)
while line do
(let* ((tab-pos (search " " line))
(left (parse-integer (subseq line 0 tab-pos)))
(right (parse-integer (subseq line (1+ tab-pos)))))
(push left left-numbers)
(push right right-numbers))))
(list
(nreverse left-numbers)
(nreverse right-numbers))))
(let* ((input-list (readlists *input/d1*))
(left (sort (first input-list) #'<))
(right (sort (second input-list) #'<))
(diff (mapcar #'- left right))
(absdiff (mapcar #'abs diff))
(result (apply #'+ absdiff)))
(print result))
; 2066446
(let* ((input-list (readlists *input/d1*))
(left (first input-list))
(right (second input-list))
(result (apply #'+ (mapcar #'(lambda (x) (* x (count x right))) left))))
(print result))
; 24931009
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