p18 done

p18/p18.org

@@ -16,7 +16,7 @@ First parse with regex to make into a list
 	height 71
 	start-pos '(0 0)
 	end-pos (list (- width 1) (- height 1)))
-  (setq data (-take 1024 data))
+  (setq full-data data)
 #+end_src
   now declare the usual helper functions
 #+begin_src emacs-lisp :results none
@@ -42,26 +42,46 @@ First parse with regex to make into a list
 	 (not (corrupted-p p))
 	 (not (visited-p p))))
 
-  (setq distances '(((0 0) . 0)))
+
 #+end_src
 
 #+begin_src emacs-lisp
-  (setq new distances)
+    (defun step (new-distances)
+      (let ((radius (1+ (cdar new-distances)))
+	    (sphere (-map #'car new-distances)))
+	(--map (cons it radius) (-filter #'admissible-p (-distinct (-mapcat (lambda (p) (--map (neighbour p it) ' ((1 0) (0 1) (-1 0) (0 -1))))
+									    sphere))))))
 
-  (defun step (new-distances)
-    (let ((radius (1+ (cdar new-distances)))
-	  (sphere (-map #'car new-distances)))
-      (--map (cons it radius) (-filter #'admissible-p (-distinct (-mapcat (lambda (p) (--map (neighbour p it) ' ((1 0) (0 1) (-1 0) (0 -1))))
-									  sphere)))))
-    )
-  (while (setq nn (step new))
-    (setq distances (-concat nn distances)
-	  new nn))
+  (defun out-p (n) 
+    (setq data (-take n full-data)
+	  distances '(((0 0) . 0)))
+    (setq new distances)
+
+    (while (setq nn (step new))
+      (setq distances (-concat nn distances)
+	    new nn))
+    (assoc end-pos distances))
+  (nth (- (bisect 'out-p 1024 (length full-data)) 1) full-data)
 
-  (cdr (assoc end-pos distances))
 #+end_src
 
 #+RESULTS:
-: 330
+| 10 | 38 |
+
+#+begin_src emacs-lisp
+  (defun bisect (pred begin end)
+    (if (eq (1+ begin) end) end
+      (let ((mid (/ (+ begin end) 2)))
+	(if (funcall pred mid) (bisect pred mid end)
+	  (bisect pred begin mid))))
+    )
+
+  (defun ddd (x)
+    (< x 138))
+
+  (bisect 'ddd 10 1000)
+    #+end_src
 
+    #+RESULTS:
+    : 138