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#!/usr/bin/sbcl --script
(defun main (filename)
(multiple-value-bind (towels stream) (parse filename)
(loop for pattern = (read-line stream nil)
while pattern
;; START PART 1
count (plusp (nconstructions pattern towels))
;; END PART 1 START PART 2
sum (nconstructions pattern towels)
;; END PART 2
finally (close stream))))
(defparameter *memo*
(let ((map (make-hash-table :test #'equal)))
(setf (gethash "" map) 1)
map))
(defun nconstructions (pattern towels)
(multiple-value-bind (count existsp) (gethash pattern *memo*)
(when existsp
(return-from nconstructions count)))
(let ((count 0))
(dolist (towel towels)
(when (string-prefix-p towel pattern)
(incf count (nconstructions (subseq pattern (length towel)) towels))))
(setf (gethash pattern *memo*) count)))
(defun string-prefix-p (prefix string)
(and (<= (length prefix) (length string))
(string= prefix (subseq string 0 (length prefix)))))
(defun parse (filename)
(let* ((stream (open filename))
(towels (parse-strings (read-line stream))))
(read-line stream) ; Consume empty line
(values towels stream)))
(defun parse-strings (string)
(loop for end = (position-if-not #'alpha-char-p string)
collect (subseq string 0 end) into strings
unless end
return strings
do (setq string (subseq string (+ 2 end)))))
(format t "~d~%" (main "input"))
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