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(ql:quickload '(fiveam uiop arrows trivia))
(defun parse-instructions (str &optional (start 0))
(multiple-value-bind (action str-pos)
(case (aref str start)
(#\R 'right)
(#\L 'left)
(t (parse-integer str :start start :junk-allowed t)))
(let ((next (or str-pos (1+ start))))
(if (= next (length str))
(list action)
(cons action (parse-instructions str next))))))
(defun create-field (filename)
(let* ((data (uiop:read-file-lines filename))
(map (butlast data 2))
(instructions (car (last data)))
(rows (length map))
(columns (loop for r in map maximize (length r)))
(field (make-array (list rows columns) :initial-element nil)))
(loop for row in map
for i from 0
do (loop for entry across row
for j from 0
do (setf (aref field i j)
(ecase entry
(#\. 'free)
(#\# 'wall)
(#\Space nil)))))
(list field (parse-instructions instructions))))
(defstruct state
x-pos y-pos direction)
(defun wrap-step (state field)
(destructuring-bind (height width) (array-dimensions field)
(with-slots (direction x-pos y-pos) state
(destructuring-bind (new-x new-y)
(ecase direction
(^ (list x-pos (mod (1- y-pos) height)))
(v (list x-pos (mod (1+ y-pos) height)))
(> (list (mod (1+ x-pos) width) y-pos))
(< (list (mod (1- x-pos) width) y-pos)))
(let ((new-state (make-state :x-pos new-x :y-pos new-y :direction direction)))
(if (aref field new-y new-x)
new-state
(wrap-step new-state field)))))))
(defun new-direction (current-direction turn &aux (directions #(^ > v <)))
(svref directions
(mod
(+
(ecase turn
(left -1)
(right 1))
(position current-direction directions))
4)))
(defun walk (field state steps advance-fn)
(if (zerop steps)
state
(let ((new-state (funcall advance-fn state field)))
(with-slots (x-pos y-pos) new-state
(ecase (aref field y-pos x-pos)
(free (walk field new-state (1- steps) advance-fn))
(wall state))))))
(defun traverse (field instructions origin advance-fn)
(let ((state (copy-structure origin)))
(dolist (move instructions state)
(if (numberp move)
(setf state (walk field state move advance-fn))
(setf (state-direction state) (new-direction (state-direction state) move))))))
(defun decode-state (state)
(with-slots (x-pos y-pos direction) state
(+ (* 1000 (1+ y-pos))
(* 4 (1+ x-pos))
(ecase direction
(> 0)
(v 1)
(< 2)
(^ 3)))))
(defun get-start (field)
(loop for i from 0
until (aref field 0 i)
finally (return i)))
(defun solver (filename advance-fn)
(destructuring-bind (field instructions) (create-field filename)
(decode-state
(traverse field instructions (make-state :x-pos (get-start field) :y-pos 0 :direction '>) advance-fn))))
;;; part 2
;;; Cube face layout
;;; 1
;;; 234
;;; 56
;;; face coords
;;; 1=2 0
;;; 2=0 1
;;; 3=1 1
;;; 4=2 1
;;; 5=2 2
;;; 6=3 2
(defparameter *example-faces*
'((1 . (2 0))
(2 . (0 1))
(3 . (1 1))
(4 . (2 1))
(5 . (2 2))
(6 . (3 2))))
(defun coord->face (x-face y-face faces)
(car (rassoc (list x-face y-face) faces :test #'equal)))
(defun face->coord (face faces)
(cdr (assoc face faces :test #'eq)))
(defun reduced-coords (state face-length faces)
(with-slots (x-pos y-pos) state
(multiple-value-bind (x-face x-coord)
(floor x-pos face-length)
(multiple-value-bind (y-face y-coord)
(floor y-pos face-length)
(list (coord->face x-face y-face faces) x-coord y-coord)))))
(defun place-state (face x y direction face-length faces)
(destructuring-bind (x-face y-face) (face->coord face faces)
(make-state :x-pos (+ x (* x-face face-length))
:y-pos (+ y (* y-face face-length)) :direction direction)))
;; The one direction from each face
;; The transitions are symetric on the position operation
;; ↱→↴
;; ↑↱1→↴
;;⬐234↴|
;;||↳56↲
;;|↳→⬏↑
;;↳→→→⬏
(defun compose (&rest funcs)
(reduce (lambda (f g)
(lambda (&rest args)
(apply f (apply g args))))
funcs))
(defun face-jump (face direction fl)
"fl is face-length"
(flet ((rot-ccw (x y) (list y (- fl 1 x)))
(rot-cw (x y) (list (- fl 1 y) x))
(cross-x (x y) (list (- fl 1 x) y))
(cross-y (x y) (list x (- fl 1 y))))
(ecase face
(1 (case direction
(> (list 6 '< (compose #'rot-cw #'rot-cw #'cross-x)))
(< (list 3 'v (compose #'rot-ccw #'cross-x)))
(v (list 4 'v #'cross-y))
(^ (list 2 'v (compose #'rot-cw #'rot-cw #'cross-y)))))
(2 (case direction
(> (list 3 '> #'cross-x))
(< (list 6 '^ (compose #'rot-cw #'cross-x)))
(v (list 5 '^ (compose #'rot-ccw #'rot-ccw #'cross-y)))
(^ (list 1 'v (compose #'rot-cw #'rot-cw #'cross-y)))))
(3 (case direction
(> (list 4 '> #'cross-x))
(< (list 2 '< #'cross-x))
(v (list 5 '> (compose #'rot-ccw #'cross-y)))
(^ (list 1 '> (compose #'rot-cw #'cross-y)))))
(4 (case direction
(> (list 6 'v (compose #'rot-cw #'cross-x)))
(< (list 3 '< #'cross-x))
(v (list 5 'v #'cross-y))
(^ (list 1 '^ #'cross-y))))
(5 (case direction
(> (list 6 '> #'cross-x))
(< (list 3 '^ (compose #'rot-cw #'cross-x)))
(v (list 2 '^ (compose #'rot-cw #'rot-cw #'cross-y)))
(^ (list 4 '^ #'cross-y))))
(6 (case direction
(> (list 1 '< (compose #'rot-ccw #'rot-ccw #'cross-x)))
(< (list 5 '< #'cross-x))
(v (list 2 '> (compose #'rot-ccw #'cross-y)))
(^ (list 4 '< (compose #'rot-ccw #'cross-y))))))))
;;; Cube face layout
;; 36
;; 4
;; 15
;; 2
(defparameter *problem-faces*
'((1 . (0 2))
(2 . (0 3))
(3 . (1 0))
(4 . (1 1))
(5 . (1 2))
(6 . (2 0))))
(defun problem-face-jump (face direction fl)
"fl is face-length"
(flet ((rot-ccw (x y) (list y (- fl 1 x)))
(rot-cw (x y) (list (- fl 1 y) x))
(cross-x (x y) (list (- fl 1 x) y))
(cross-y (x y) (list x (- fl 1 y))))
(ecase face
(1 (case direction
(> (list 5 '> #'cross-x))
(< (list 3 '> (compose #'rot-cw #'rot-cw #'cross-x)))
(v (list 2 'v #'cross-y))
(^ (list 4 '> (compose #'rot-cw #'cross-y)))))
(2 (case direction
(> (list 5 '^ (compose #'rot-ccw #'cross-x)))
(< (list 3 'v (compose #'rot-cw #'rot-cw #'rot-cw #'cross-x)))
(v (list 6 'v #'cross-y))
(^ (list 1 '^ #'cross-y))))
(3 (case direction
(> (list 6 '> #'cross-x))
(< (list 1 '> (compose #'rot-cw #'rot-cw #'cross-x)))
(v (list 4 'v #'cross-y))
(^ (list 2 '> (compose #'rot-ccw #'rot-ccw #'rot-ccw #'cross-y)))))
(4 (case direction
(> (list 6 '^ (compose #'rot-ccw #'cross-x)))
(< (list 1 'v (compose #'rot-ccw #'cross-x)))
(v (list 5 'v #'cross-y))
(^ (list 3 '^ #'cross-y))))
(5 (case direction
(> (list 6 '< (compose #'rot-ccw #'rot-ccw #'cross-x)))
(< (list 1 '< #'cross-x))
(v (list 2 '< (compose #'rot-cw #'cross-y)))
(^ (list 4 '^ #'cross-y))))
(6 (case direction
(> (list 5 '< (compose #'rot-cw #'rot-cw #'cross-x)))
(< (list 3 '< #'cross-x))
(v (list 4 '< (compose #'rot-cw #'cross-y)))
(^ (list 2 '^ #'cross-y)))))))
(defun cube-step (state face-length jumper faces)
(destructuring-bind (face x-coord y-coord) (reduced-coords state face-length faces)
(with-slots (direction) state
(let ((new-x (+ x-coord (case direction (< -1) (> 1) (t 0))))
(new-y (+ y-coord (case direction (^ -1) (v 1) (t 0)))))
(if (and
(< -1 new-x face-length)
(< -1 new-y face-length))
(place-state face new-x new-y direction face-length faces)
(destructuring-bind (new-face new-direction pos-fn) (funcall jumper face direction face-length)
(destructuring-bind (new-x new-y) (funcall pos-fn x-coord y-coord)
(place-state new-face new-x new-y new-direction face-length faces))))))))
(defun copy-clear-field (field)
(destructuring-bind (height width) (array-dimensions field)
(let ((new-field (make-array (list height width) :initial-element nil)))
(loop for y below height
do (loop for x below width when (aref field y x) do (setf (aref new-field y x) 'free)))
new-field)))
(fiveam:test preparation
(fiveam:is (eq 'v (new-direction '> 'right)))
(fiveam:is (eq '< (new-direction '^ 'left)))
(fiveam:is (equal
(parse-instructions "10R5L5R10L4R5L5" )
'(10 RIGHT 5 LEFT 5 RIGHT 10 LEFT 4 RIGHT 5 LEFT 5)))
(fiveam:is (= 1 (coord->face 2 0 *example-faces*)))
(fiveam:is (= 6 (apply #'coord->face (append (face->coord 6 *example-faces*) (list *example-faces*))))))
(defun cube-stepper (jumper faces face-length)
(lambda (state field) (declare (ignore field))
(cube-step state face-length jumper faces)))
(fiveam:test around-cube
(loop for (field jumper faces face-length) in (list (list (copy-clear-field (car (create-field "eg-in")))
#'face-jump *example-faces* 4)
(list (copy-clear-field (car (create-field "input")))
#'problem-face-jump *problem-faces* 50))
do (flet ((check (origin moves advance-fn)
(equalp origin
(traverse field moves
origin advance-fn))))
(dotimes (i 6) ;; on each face
(let ((origin (place-state (1+ i) 0 0 '^ face-length faces))
(stepper (cube-stepper jumper faces face-length)))
;; around corners
(fiveam:is (check origin '(1 left 1 left 1 left) stepper))
;; walk all dirs straight
(dolist (dir '(> v < ^))
(fiveam:is (check origin (list (* 4 face-length)) stepper))))))))
(fiveam:test solutions
(fiveam:is (= 6032 (solver "eg-in" #'wrap-step)))
(fiveam:is (= 159034 (solver "input" #'wrap-step)))
;; part 2
(fiveam:is (= 5031 (solver "eg-in" (cube-stepper #'face-jump *example-faces* 4))))
(fiveam:is (= 147245 (solver "input" (cube-stepper #'problem-face-jump *problem-faces* 50)))))
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