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#!/usr/bin/sbcl --script
(load "heap.lisp")
(defstruct dnode
(x nil :type integer)
(y nil :type integer)
(dir nil :type integer)
(seen nil :type list))
(defun main (filename)
(multiple-value-call #'dijkstra (parse-maze filename)))
(defun dijkstra (maze beg end)
(let* ((directions #2A((0 -1) (+1 0) (0 +1) (-1 0)))
(cost-table (make-hash-table :test #'dnode=))
(to-visit (heap:make-heap :priority-function #'cdr))
(lowest-score most-positive-fixnum)
seen-tiles)
(flet ((get-cost (node) (or (gethash node cost-table)
most-positive-fixnum)))
(heap:enqueue (cons (make-dnode :x (car beg) :y (cdr beg)
:dir 1 :seen (list beg))
0)
to-visit)
(loop
(let* ((pair (heap:dequeue to-visit))
(node (car pair))
(cost (cdr pair))
(dir (dnode-dir node))
(seen (dnode-seen node)))
(when (> cost lowest-score)
;; START PART 1
(return-from dijkstra cost)
;; END PART 1 START PART 2
(return-from dijkstra (length seen-tiles))
;; END PART 2
)
(unless (< (get-cost node) cost)
(setf (gethash node cost-table) cost)
(dolist (d (list dir (mod (1- dir) 4) (mod (1+ dir) 4)))
(let* ((x (+ (dnode-x node) (aref directions d 0)))
(y (+ (dnode-y node) (aref directions d 1)))
(nseen (adjoin (cons x y) seen :test #'equal))
(nnode (make-dnode :x x :y y :dir d :seen nseen))
(ncost (+ cost (if (= d dir) 1 1001))))
(when (and (<= ncost (get-cost nnode))
(dnode-pos-valid-p nnode maze))
(if (equal (cons x y) end)
(setq lowest-score ncost
seen-tiles (union seen-tiles nseen :test #'equal))
(progn
(setf (gethash nnode cost-table) ncost)
(heap:enqueue (cons nnode ncost) to-visit))))))))))))
(defun dnode= (x y)
(and (= (dnode-x x) (dnode-x y))
(= (dnode-y x) (dnode-y y))
(= (dnode-dir x) (dnode-dir y))))
(defun sxhash-dnode (node)
(sxhash (list (dnode-x node)
(dnode-y node)
(dnode-dir node))))
(define-hash-table-test dnode= sxhash-dnode)
(defun dnode-pos-valid-p (node maze)
(destructuring-bind (my mx) (array-dimensions maze)
(let ((nx (dnode-x node))
(ny (dnode-y node)))
(and (< -1 nx mx)
(< -1 ny my)
(char/= #\# (aref maze ny nx))))))
(defun parse-maze (filename)
(with-open-file (stream filename)
(multiple-value-bind (lines line-count beg end)
(loop with beg = 0
with end = 0
for line = (read-line stream nil)
for line-count upfrom 0
while line
for s-pos = (position #\S line)
for e-pos = (position #\E line)
if s-pos
do (setq beg (cons s-pos line-count))
if e-pos
do (setq end (cons e-pos line-count))
collect line into lines
finally (return (values lines line-count beg end)))
(values
(make-array (list line-count (length (first lines)))
:element-type 'character
:initial-contents lines)
beg end))))
(format t "~d~%" (main "input"))
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