From 9978ef9367566fdea7bded0ebb7eb3a4857fcb2f Mon Sep 17 00:00:00 2001
From: Jacopo De Simoi <wilderjds@protonmail.com>
Date: Thu, 17 Apr 2025 16:28:49 -0400
Subject: [PATCH] New attempt

---
 p16/p16.org | 65 +++++++++++++++++++++++++++++++++++++----------------
 1 file changed, 46 insertions(+), 19 deletions(-)

diff --git a/p16/p16.org b/p16/p16.org
index 8674ace..e307d96 100644
--- a/p16/p16.org
+++ b/p16/p16.org
@@ -4,7 +4,7 @@ Load map
 #+begin_src emacs-lisp :results none
   (require 'dash)
   (with-temp-buffer
-      (insert-file-contents "input-test2")
+      (insert-file-contents "input")
       (goto-char (point-min))
       (replace-regexp "^\\(#.*#\\)$" "\"\\1\"")
       (goto-char (point-min))
@@ -75,45 +75,72 @@ associated scores;
   (explore start '(1 0) 0)
 #+end_src
 
+For debugging, print the map
+#+begin_src emacs-lisp
+    (defun plot (p s)
+      (goto-line (+ (cadr p) 1))
+      (move-to-column (car p))
+      (insert s)
+      (delete-char 1))
+
+  (defun print-map (p)
+    (with-temp-buffer
+      (-each data (lambda (x) (insert x) (insert "\n")))
+      (-each book (lambda (x) (if (cdr x) (plot (caar x) ?x)
+                                (plot (caar x) ?!))))
+      (plot p ?@)
+      (write-file "tmp")) )
+
+
+#+end_src
+
+#+RESULTS:
+: print-map
+
 In principle the above would work as-is, but it is not very efficient.
 In the version below, we record dead-ends and partial solutions
 #+begin_src emacs-lisp
   (defun >nil (a b)
-    (when b
-      (or (not a) (> a b))))
+    (when (numberp b)
+      (or (not (numberp a)) (> a b))))
 
   (defun subtract-nil (a b)
-    (when (and a b)
+    (when (and (numberp a) (numberp b))
       (- a b)))
 
   (defun +nil (a b)
-    (when (and a b)
+    (when (and (numberp a) (numberp b))
       (+ a b)))
 
   (defun neighbour-maybe (p dir newdir)
     (if (not (equal dir newdir)) p
       (neighbour p newdir)))
 
-  (defun explore (p dir score &optional past)
+  (defun forward-dirs (dir olddir)
+    (if (not (equal dir olddir)) (list dir)
+      (cons dir (--filter (= (dot it dir) 0) '((0 1) (0 -1) (-1 0) (1 0))))))
+
+  (defun explore (p dir old-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) score
       (if (assoc (list p dir) book) (+nil score (cdr (assoc (list p dir) book))) ; check the book for this position and direction
-       (unless (-contains-p (cdr 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))
-                (new-score (-min-by #'>nil (-map (lambda (newdir)
-                                                   (explore (neighbour-maybe p dir newdir) newdir
-                                                            (+ score (if (equal newdir dir) 1 1000))
-                                                            (cons p past)))
-                                                 acceptable-dirs))))
-           (push (cons (list p dir) (subtract-nil new-score score)) book)
-           new-score)))))
-
-  (setq book nil)
-  (explore start '(1 0) 0)
+        (if (-contains-p (cdr past) p) 'loop
+          (let* ((acceptable-dirs (--filter (not (eq (thing-at (neighbour p it)) 'wall)) (forward-dirs dir old-dir)))
+                 (new-score (-min-by #'>nil (-map (lambda (newdir)
+                                                    (explore (neighbour-maybe p dir newdir) newdir dir
+                                                             (+ score (if (equal newdir dir) 1 1000))
+                                                             (-distinct (cons p past))))
+                                                  acceptable-dirs))))
+            (when (not (eq new-score 'loop)) (push (cons (list p dir) (subtract-nil new-score score)) book))
+            new-score)))))
+
+    (setq book nil)
+    (explore start '(1 0) '(1 0) 0)
   #+end_src
 
 #+RESULTS:
 : 11048
+
+(print-map)