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(ql:quickload '(fiveam str))
;12:13
;
(defparameter eg-input "LLR
AAA = (BBB, BBB)
BBB = (AAA, ZZZ)
ZZZ = (ZZZ, ZZZ)")
(defun parse-input (lines)
(let ((graph (make-hash-table)))
(destructuring-bind (instructions blank . nodes) lines
(declare (ignorable blank))
(dolist (line nodes)
(with-input-from-string (in (str:replace-all "=|," "" line :regex t))
(setf
(gethash (read in) graph)
(read in))))
(values instructions graph))))
(defun traverse (instructions graph location steps)
(if (eq location 'ZZZ)
(values steps location)
(let ((new-steps (loop
for direction across instructions
do
(setf location
(ecase direction
(#\L (first (gethash location graph)))
(#\R (second (gethash location graph)))))
count direction until (eq location 'ZZZ))))
(traverse instructions graph location (+ steps new-steps)))))
(defun solver1 (lines)
(multiple-value-bind (instructions graph)
(parse-input lines)
(traverse instructions graph 'AAA 0)))
(fiveam:test solutions
(fiveam:is (= 6 (solver1 (uiop:split-string eg-input :separator '(#\Newline)))))
(fiveam:is (= 19199 (solver1 (uiop:read-file-lines "input")))))
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