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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 (reduce (lambda (a r) (max a (length r))) map :initial-value 0))
(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)))))
(values field (parse-instructions instructions))))
(defun get-start (field)
(loop for i from 0
until (aref field 0 i)
finally (return i)))
(defstruct state
x-pos y-pos direction)
(defun advance (field state)
(destructuring-bind (height width) (array-dimensions field)
(with-slots (direction x-pos y-pos) state
(destructuring-bind (new-x new-y)
(ecase direction
(north (list x-pos (mod (1- y-pos) height)))
(south (list x-pos (mod (1+ y-pos) height)))
(east (list (mod (1+ x-pos) width) y-pos))
(west (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
(advance field new-state)))))))
(defconstant +directions+ #(north east south west))
(defun new-direction (current-direction turn)
(svref +directions+
(mod
(+
(ecase turn
(left -1)
(right 1))
(position current-direction +directions+))
4)))
(defun walk (field state steps)
(if (zerop steps)
state
(let ((new-state (advance field state)))
(with-slots (x-pos y-pos) new-state
(ecase (aref field y-pos x-pos)
(free (walk field new-state (1- steps)))
(wall state))))))
(fiveam:test preparation
(fiveam:is (eq 'south (new-direction 'east 'right)))
(fiveam:is (eq 'west (new-direction 'north 'left)))
(fiveam:is (equal
(parse-instructions "10R5L5R10L4R5L5" )
'(10 RIGHT 5 LEFT 5 RIGHT 10 LEFT 4 RIGHT 5 LEFT 5))))
(defun decode-state (state)
(with-slots (x-pos y-pos direction) state
(+ (* 1000 (1+ y-pos))
(* 4 (1+ x-pos))
(ecase direction
(east 0)
(south 1)
(west 2)
(north 3)))))
(defun solver (filename)
(multiple-value-bind (field instructions) (create-field filename)
(let ((state (make-state :x-pos (get-start field) :y-pos 0 :direction 'east)))
(dolist (move instructions)
(if (numberp move)
(setf state (walk field state move))
(setf (state-direction state) (new-direction (state-direction state) move))))
(decode-state state))))
(fiveam:test solutions
(fiveam:is (= 6032 (solver "eg-in")))
(fiveam:is (= 159034 (solver "input"))))
(defun face-coords (state face-length)
(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 x-face y-face x-coord y-coord)))))
(defun cube-advance (field state face-length)
(destructuring-bind (x-face y-face x-coord y-coord) (face-coords state (floor (array-dimension field 0) 3))
(let ((new-x (+ x-coord (case direction (< -1) (> 1) (t 0))))
(new-y (+ y-coord (case direction (^ -1) (v 1) (t 0))))))
(if (and
(<= 0 new-x face-length)
(<= 0 new-y face-length))
(make-state :x-pos (+ new-x (* x-face face-length))
:y-pos (+ new-y (* y-face face-length)) :direction direction))
(with-slots (direction x-pos y-pos) state
(floor (+ x-pos
(case direction (< -1) (> 1) (t 0)))
face-length)
(floor (+ y-pos
(case direction (^ -1) (v 1) (t 0)))
face-lendth)
(destructuring-bind (new-x new-y)
(case direction
(^ -1) (list x-pos (floor (1- y-pos) face-length))
(v 1) (list x-pos (floor (1+ y-pos) face-length))
(> 1) (list (floor (1+ x-pos) face-length) y-pos)
(< -1) (list (floor (1- x-pos) face-length) 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
(cube-advance field new-state)))))))
(values (values 5 6) (values 9 2))
(floor (array-dimension (create-field "eg-in") 0) 3)
(let ((a 5))
(trivia:match (list 5 6 2)
((trivia:guard (list 5 op 2)
(= op (1+ a))) 'hu)))
;;; 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
(trivia:match (list x-face y-face direction)
;; Face 1
((list 2 0 '>) (list 3 2 '<)) ;; 1-6
((list 2 0 'v) (list 2 1 'v)) ;; 1-4
((list 2 0 '<) (list 1 1 'v)) ;; 1-3
((list 2 0 '^) (list 0 1 'v)) ;; 1-2
;; Face 2
((list 0 1 '>) (list 1 1 '>)) ;; 2-3
((list 0 1 'v) (list 2 2 '^)) ;; 2-5
((list 0 1 '<) (list 3 2 '^)) ;; 2-6
((list 0 1 '^) (list 2 0 'v)) ;; 2-1
;; Face 3
((list 1 1 '>) (list 2 1 '>)) ;; 3-4
((list 1 1 'v) (list 2 2 '>)) ;; 3-5
((list 1 1 '<) (list 0 1 '<)) ;; 3-2
((list 1 1 '^) (list 2 0 '>)) ;; 3-1
;; Face 4
((list 2 1 '>) (list 3 2 'v)) ;; 4-6
((list 2 1 'v) (list 2 2 'v)) ;; 4-5
((list 2 1 '<) (list 1 1 '<)) ;; 4-3
((list 2 1 '^) (list 2 0 '^)) ;; 4-1
;; Face 5
((list 2 2 '>) (list 3 2 '>)) ;; 5-6
((list 2 2 'v) (list 0 1 '^)) ;; 5-2
((list 2 2 '<) (list 1 1 '^)) ;; 5-3
((list 2 2 '^) (list 2 1 '^)) ;; 5-4
;; Face 6
((list 3 2 '>) (list 2 0 '<)) ;; 6-1
((list 3 2 'v) (list 0 1 '>)) ;; 6-2
((list 3 2 '<) (list 2 2 '<)) ;; 6-5
((list 3 2 '^) (list 2 1 '<)) ;; 6-4
)
(trivia:match '(> 5)
((list '> op) 6))
(let ((fl 4))
(destructuring-bind (x-face y-face x-coord y-coord) (list 2 0 -1 1)
(trivia:match (list x-face y-face x-coord y-coord)
;; Face 1 to its 4 neighbors 6,4,3,2
((trivia:guard
(list 2 0 x y) ;; Neighbor 6
(= (* 3 fl) x))
(make-state :x-pos (1- (* 4 fl)) :y-pos (- (* 3 fl) y 1) :direction '<))
((trivia:guard ;; neighbor 4 is contiguous; no change
(list 2 0 x y)
(= fl y))
(make-state :x-pos (+ x (* 2 fl)) :y-pos fl :direction 'v))
((list 2 0 -1 y) ;; Neighbor 3
(make-state :x-pos (+ y fl) :y-pos fl :direction 'v))
((list 2 0 x -1) ;; neighbor 2
(make-state :x-pos (- fl x) :y-pos fl :direction 'v))
;; Face 2 to its 4 neighbors 3,5,6,1
((trivia:guard ;; Neighbor 3 contiguous
(list 0 1 x y)
(= x fl))
(make-state :x-pos fl :y-pos (+ y fl) :direction '>))
((trivia:guard ;; Neighbor 5
(list 0 1 x y)
(= y (* 2 fl)))
(make-state :x-pos (- fl x 1) :y-pos (1- (* 3 fl)) :direction '^))
)))
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