Resolved merge.

advent-of-code-2018.asd

@@ -6,7 +6,7 @@
   :license  "Specify license here"
   :version "0.0.1"
   :serial t
-  :depends-on ("cl-ppcre" "drakma")
+  :depends-on ("cl-ppcre" "drakma" "cl-heap")
   :components ((:file "package")
                (:file "utilities")
                (:file "day1")
@@ -28,4 +28,6 @@
                (:file "day18")
                (:file "day19")
                (:file "day23")
-               (:file "day25")))
+               (:file "day25")
+               (:file "day20")))
+

day20.lisp

@@ -0,0 +1,80 @@
+;;;; day20.lisp
+
+(in-package :advent-of-code-2018)
+
+(defun day20-parse-file (&optional (file (puzzlefile 20)))
+  (with-open-file (in file)
+    (labels ((parse-group ()
+               (loop
+                 :with result := nil
+                 :with option := nil
+                 :with seq := nil
+                 :for char := (read-char in)
+                 :do (case char
+                       ((#\N #\S #\W #\E) (push char seq))
+                       (#\(
+                        (unless (null seq)
+                          (push (coerce (nreverse seq) 'string) option)
+                          (setf seq nil))
+                        (push (parse-group) option))
+                       ((#\) #\$)
+                        (unless (null seq)
+                          (push (coerce (nreverse seq) 'string) option))
+                        (when (null option)
+                          (push "" option))
+                        (push (nreverse option) result)
+                        (return (nreverse result)))
+                       (#\|
+                        (unless (null seq)
+                          (push (coerce (nreverse seq) 'string) option)
+                          (setf seq nil))
+                        (when (null option)
+                          (push "" option))
+                        (push (nreverse option) result)
+                        (setf option nil))))))
+      (read-char in)
+      (first (parse-group)))))
+
+(defun day20-build-graph (node)
+  (let ((edges (make-hash-table)))
+    (labels ((move (current char)
+               (let* ((shift
+                        (case char
+                          (#\N #C( 0  1))
+                          (#\E #C( 1  0))
+                          (#\S #C( 0 -1))
+                          (#\W #C(-1  0))
+                          (t 0)))
+                      (next (mapcar (lambda (pos) (+ pos shift)) current)))
+                 (loop :for room1 :in current
+                       :for room2 :in next
+                       :do (pushnew room2 (gethash room1 edges nil))
+                       :do (pushnew room1 (gethash room2 edges nil)))
+                 next))
+             (follow (current path)
+               (loop :for c :across path
+                     :for new := (move current c) :then (move new c)
+                     :finally (return new)))
+             (explore-seq (current node)
+               (loop :for path :in node
+                     :when (stringp path) :do (setf current (follow current path))
+                     :else :do (explore-options current path)))
+             (explore-options (current options)
+               (loop :for option :in options
+                     :when (stringp option) :nconc (follow current option)
+                     :else :nconc (explore-seq current option))))
+      (explore-seq (list #C(0 0)) node))
+    edges))
+
+(defun day20 ()
+  (let ((edges (day20-build-graph (day20-parse-file))))
+    (loop :with open := (make-instance 'fibonacci-heap :key #'car)
+          :with closed := (make-hash-table)
+          :for (depth . node) := (cons 0 #C(0 0)) :then (pop-heap open)
+          :count (>= depth 1000) :into far-away
+          :do (setf (gethash node closed) t)
+          :do (dolist (new (gethash node edges))
+                (unless (gethash new closed nil)
+                  (add-to-heap open (cons (1+ depth) new))))
+          :while (> (heap-size open) 0)
+          :finally (format t "The furthest room is ~a doors away and there a total of ~a rooms 1000 doors or more away.~%" depth far-away))))