[p18] cleanup code

p18/p18.org

@@ -18,70 +18,66 @@ First parse with regex to make into a list
 	end-pos (list (- width 1) (- height 1)))
   (setq full-data data)
 #+end_src
-  now declare the usual helper functions
+  Now define the usual helper functions
 #+begin_src emacs-lisp :results none
-      (defun neighbour (p dir)
-	"Returns the neighbour to P in the direction DIR"
-	(list (+ (car p) (car dir))
-	      (+ (cadr p) (cadr dir))))
+  (defun neighbour (p dir)
+    "Returns the neighbour to P in the direction DIR"
+    (list (+ (car p) (car dir))
+	  (+ (cadr p) (cadr dir))))
 
-      (defun within-bounds-p (p)
-	(let ((x (car p))
-	      (y (cadr p)))
-	  (and (>= x 0) (< x width)
-	       (>= y 0) (< y height))))
+  (defun within-bounds-p (p)
+    (let ((x (car p))
+	  (y (cadr p)))
+      (and (>= x 0) (< x width)
+	   (>= y 0) (< y height))))
 
-      (defun corrupted-p (p)
-	(-contains-p data p))
+  (defun corrupted-p (p)
+    (-contains-p data p))
 
-      (defun visited-p (p)
-	(-contains-p (-map #'car distances) p)) 
+  (defun visited-p (p)
+    (-contains-p (-map #'car distances) p)) 
 
   (defun admissible-p (p)
     (and (within-bounds-p p)
 	 (not (corrupted-p p))
 	 (not (visited-p p))))
+#+end_src
 
-
+Define a generic bisect function
+#+begin_src emacs-lisp :results none
+  (defun bisect (pred begin end)
+    "returns the first n between BEGIN and END such that PRED n is nil"
+    (if (eq (1+ begin) end) end
+      (let ((mid (/ (+ begin end) 2)))
+	(if (funcall pred mid) (bisect pred mid end)
+	  (bisect pred begin mid)))))
 #+end_src
 
+Now solve the problem
 #+begin_src emacs-lisp
-    (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))))))
 
   (defun out-p (n) 
-    (setq data (-take n full-data)
-	  distances '(((0 0) . 0)))
-    (setq new distances)
+    (let* ((data (-take n full-data))
+	  (distances '(((0 0) . 0)))
+	  (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)
+      (while (setq new (step new))
+	(setq distances (-concat new distances)))
+      (assoc end-pos distances)))
+
+  ;for part 1
+  (out-p 1024)
 
+  ;for part 2
+  (nth (- (bisect 'out-p 1024 (length full-data)) 1) full-data)
 #+end_src
 
 #+RESULTS:
 | 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