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;; 17:04
;; 17:34 part1
(ql:quickload '(fiveam str arrows))
(defparameter eg-in "rn=1,cm-,qp=3,cm=2,qp-,pc=4,ot=9,ab=5,pc-,pc=6,ot=7")
(defun hash (str)
(reduce
(lambda (acc c)
(mod (* 17 (+ acc (char-code c))) 256))
str :initial-value 0))
(defun solve1 (in)
(reduce #'+
(str:split "," (str:trim in))
:key #'hash))
(defun implement-instructions (instructions &aux (boxes (make-array 256 :initial-element nil)))
(cl-ppcre:do-register-groups (label operator (#'parse-integer focal-length))
("(\\w+)([=-])(\\d+)?" instructions)
(let ((content
(aref boxes (hash label))))
(flet ((is-lens (c) (equal (car c) label)))
(arrows:->>
(cond
((equal "-" operator)
(remove-if #'is-lens content))
((equal "=" operator)
(if (zerop (count-if #'is-lens content))
(append content (list (cons label focal-length)))
(mapcar
(lambda (c) (if (is-lens c)
(cons label focal-length)
c))
content))))
(setf (aref boxes (hash label)))))))
boxes)
(defun focusing-power (boxes)
(loop for i from 1
for lenses across boxes
sum
(* i (loop for j from 1
for (l . fl) in lenses
sum (* j fl)))))
(fiveam:test solutions
(fiveam:is (= 52 (hash "HASH")))
(fiveam:is (= 1320 (solve1 eg-in)))
(fiveam:is (= 506437 (solve1 (uiop:read-file-string "input"))))
(fiveam:is (= 145 (focusing-power (implement-instructions eg-in))))
(fiveam:is (= 288521 (focusing-power (implement-instructions (uiop:read-file-string "input"))))))
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