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(defun solver (marker-size)
(with-open-file (in "input" :element-type 'unsigned-byte)
(loop with acc = (make-array marker-size :element-type 'unsigned-byte)
for char = (ash 1 (- (read-byte in) 96)) ;; all lowercase letters thus subtract ascii start
and idx from 1
do (setf (aref acc (mod idx marker-size)) char)
when (<= marker-size (logcount (reduce (lambda (set v) (logxor set v)) acc)))
return idx)))
(ql:quickload :fiveam)
(fiveam:test results
(fiveam:is (= 1655 (solver 4)))
(fiveam:is (= 2665 (solver 14))))
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