work on p16 - more efficient

p16/p16.org

@@ -4,7 +4,7 @@ Load map
 #+begin_src emacs-lisp :results none
   (require 'dash)
   (with-temp-buffer
-      (insert-file-contents "input")
+      (insert-file-contents "input-test")
       (goto-char (point-min))
       (replace-regexp "^\\(#.*#\\)$" "\"\\1\"")
       (goto-char (point-min))
@@ -53,20 +53,28 @@ Define some aux functions
 Now, explore the maze; this function returns a list of paths and the
 associated scores;
 #+begin_src emacs-lisp
-  (defun explore (p dir &optional score past)
-  "Explore the maze starting at position P and in the direction
+  (defun >nil (a b)
+    (when b
+      (or (not a) (> a b))))
+
+  (defun +nil (a b) ;we only need a binary operator
+    (when (not ))
+    )
+
+  (defun explore (p dir score &optional past)
+    "Explore the maze starting at position P and in the direction
   DIR. Returns nil if we will dead-end or loop or the score
   if we reach the end"
-  (if (eq (thing-at p) 'end) (list score)
-    (unless (-contains-p past p)          ; loop
-      (let* ((forward-dirs (--filter (>= (dot it dir) 0)
-                                     '((0 1) (0 -1) (-1 0) (1 0))))
-             (acceptable-dirs (--filter (not (eq (thing-at (neighbour p it)) 'wall)) forward-dirs)))
-        (-mapcat (lambda (newdir)
-                   (explore (neighbour p newdir) newdir
-                            (+ score (if (equal newdir dir) 1 1001))
-                            (cons p past)))
-                 acceptable-dirs)))))
+    (if (eq (thing-at p) 'end) score
+      (unless (-contains-p past p)	; loop
+	(let* ((forward-dirs (--filter (>= (dot it dir) 0)
+				       '((0 1) (0 -1) (-1 0) (1 0))))
+	       (acceptable-dirs (--filter (not (eq (thing-at (neighbour p it)) 'wall)) forward-dirs)))
+	  (-min-by #'>nil (-map (lambda (newdir)
+				  (explore (neighbour p newdir) newdir
+					   (+ score (if (equal newdir dir) 1 1001))
+					   (cons p past)))
+				acceptable-dirs))))))
 
   (explore start '(1 0) 0)
 #+end_src