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#!/usr/bin/sbcl --script
(defparameter *map* nil)
(defparameter *moves* nil)
(defparameter *robot-pos* nil)
(defun main (filename)
(parse-input filename)
(mapc #'handle-move *moves*)
(loop with (my mx) = (array-dimensions *map*)
for y from 0 below my
sum (loop for x from 0 below mx
if (box-at-pos-p (cons x y))
sum (+ x (* 100 y)))))
(defun handle-move (v⃗)
(when (can-move-p v⃗)
(map-setf *robot-pos* #\.)
(setq *robot-pos* (vec2+ *robot-pos* v⃗))
(let ((dest-char (aref-vec2 *map* *robot-pos*)))
(case dest-char
(#\[ (handle-box-move *robot-pos* v⃗))
(#\] (handle-box-move (left-of *robot-pos*) v⃗))))
(map-setf *robot-pos* #\@)))
(defun handle-box-move (pos v⃗)
(cond
((equal v⃗ '(+1 . 0))
(let ((next-box-pos (right-of pos 2)))
(when (box-at-pos-p next-box-pos)
(handle-box-move next-box-pos v⃗)))
(map-setf (right-of pos 1) #\[)
(map-setf (right-of pos 2) #\]))
((equal v⃗ '(-1 . 0))
(let ((next-box-pos (left-of pos 2)))
(when (box-at-pos-p next-box-pos)
(handle-box-move next-box-pos v⃗)))
(map-setf pos #\])
(map-setf (left-of pos) #\[))
(:else ; (or (equal v⃗ '(0 . +1)) (equal v⃗ '(0 . -1)))
(let* ((dy (cdr v⃗))
(charl (aref-vec2 *map* (vec2+ pos (cons 0 dy))))
(charr (aref-vec2 *map* (vec2+ pos (cons 1 dy)))))
(when (char= charl #\[)
(handle-box-move (vec2+ pos v⃗) v⃗))
(when (char= charl #\])
(handle-box-move (vec2+ pos (cons -1 dy)) v⃗))
(when (char= charr #\[)
(handle-box-move (vec2+ pos (cons +1 dy)) v⃗))
(map-setf pos #\.)
(map-setf (right-of pos) #\.)
(map-setf (vec2+ pos (cons 0 dy)) #\[)
(map-setf (vec2+ pos (cons 1 dy)) #\])))))
(defun box-at-pos-p (pos)
(char= (aref-vec2 *map* pos) #\[))
(defun can-move-p (v⃗)
(let ((pos (vec2+ *robot-pos* v⃗)))
(ecase (aref-vec2 *map* pos)
(#\. t)
(#\# nil)
(#\[ (can-move-box-p pos v⃗))
(#\] (can-move-box-p (left-of pos) v⃗)))))
(defun can-move-box-p (pos v⃗)
(cond
((equal v⃗ '(1 . 0))
(let ((next-box-pos (right-of pos 2)))
(ecase (aref-vec2 *map* next-box-pos)
(#\. t)
(#\# nil)
(#\[ (can-move-box-p next-box-pos v⃗)))))
((equal v⃗ '(-1 . 0))
(ecase (aref-vec2 *map* (left-of pos))
(#\. t)
(#\# nil)
(#\[
(print *map*)
(quit))
(#\] (can-move-box-p (left-of pos 2) v⃗))))
(:else ; (or (equal v⃗ '(0 . +1)) (equal v⃗ '(0 . -1)))
(let* ((dy (cdr v⃗))
(charl (aref-vec2 *map* (vec2+ pos (cons 0 dy))))
(charr (aref-vec2 *map* (vec2+ pos (cons 1 dy)))))
(cond ((char= #\. charl charr)
t)
((or (char= #\# charl)
(char= #\# charr))
nil)
((char= #\[ charl)
(can-move-box-p (vec2+ pos v⃗) v⃗))
(:else ; (or (char= #\] charl) (char= #\[ charr))
(and (or (char/= #\] charl)
(can-move-box-p (vec2+ pos (cons -1 dy)) v⃗))
(or (char/= #\[ charr)
(can-move-box-p (vec2+ pos (cons +1 dy)) v⃗)))))))))
(defun in-map-bounds-p (pos)
(destructuring-bind (y x) (array-dimensions *map*)
(and (< -1 (car pos) x)
(< -1 (cdr pos) y))))
(defun aref-vec2 (array v⃗)
(aref array (cdr v⃗) (car v⃗)))
(defun map-setf (pos val)
(setf (aref *map* (cdr pos) (car pos)) val))
;;; 2D Vectors
(defun vec2+ (v⃗ u⃗)
(cons (+ (car v⃗) (car u⃗))
(+ (cdr v⃗) (cdr u⃗))))
(defun left-of (v⃗ &optional (n 1))
(vec2+ v⃗ (cons (- n) 0)))
(defun right-of (v⃗ &optional (n 1))
(vec2+ v⃗ (cons n 0)))
(defun up-from (v⃗ &optional (n 1))
(vec2+ v⃗ (cons 0 (- n))))
(defun down-from (v⃗ &optional (n 1))
(vec2+ v⃗ (cons 0 n)))
;;; Parsing
(defun parse-input (filename)
(with-open-file (stream filename)
(let ((contents (make-string (file-length stream))))
(read-sequence contents stream)
(destructuring-bind (map moves)
(split-string contents (format nil "~%~%"))
(multiple-value-bind (map start-pos) (parse-map map)
(setq *map* map
*moves* (parse-moves moves)
*robot-pos* start-pos))))))
(defun parse-map (string)
(let* ((first-newline (position #\Newline string))
(line-length (1+ first-newline))
(line-count (/ (1+ (length string)) line-length))
(map (make-array (list line-count (* 2 first-newline))
:element-type 'character))
start-pos)
(dotimes (y line-count)
(loop with start = (* y line-length)
for char across (subseq string start (+ start first-newline))
for x = 0 then (+ x 2)
do (ecase char
(#\# (setf (aref map y (+ 0 x)) #\#
(aref map y (+ 1 x)) #\#))
(#\O (setf (aref map y (+ 0 x)) #\[
(aref map y (+ 1 x)) #\]))
(#\. (setf (aref map y (+ 0 x)) #\.
(aref map y (+ 1 x)) #\.))
(#\@ (setf (aref map y (+ 0 x)) #\@
(aref map y (+ 1 x)) #\.
start-pos (cons x y))))))
(values map start-pos)))
(defun parse-moves (string)
(loop for char across string
unless (char= char #\Newline)
collect (ecase char
(#\^ '(0 . -1))
(#\v '(0 . +1))
(#\< '(-1 . 0))
(#\> '(+1 . 0)))))
(defun split-string (string delimiter)
(loop with delimiter-length = (length delimiter)
for end = (search delimiter string)
unless (eq end 0)
collect (subseq string 0 end) into parts
unless end
return parts
do (setq string (subseq string (+ end delimiter-length)))))
(format t "~d~%" (main "input"))
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