[lib] Move some helpers to the library

lib/lib-advent.org

@@ -32,3 +32,22 @@
                                                (-map-indexed (lambda (x el) (list el (list x y))) l))
                                              li)))))
   #+end_src
+* 2D geometry auxiliary functions
+  Here a vector is just a list with two components; the "dot"
+  function is a bit of an overkill tbh
+
+  #+begin_src emacs-lisp :results none
+  (defun advent/dot (a b)
+    "Return the dot product of the two vectors"
+    (-reduce #'+ (-map (lambda (x) (* (car x) (cdr x))) (-zip-pair a b))))
+
+  (defun advent/neighbour (p dir)
+    "Returns the neighbour to P in the direction DIR"
+    (list (+ (car p) (car dir))
+          (+ (cadr p) (cadr dir))))
+
+  (defun advent/taxicab-distance (p q)
+    "Returns the taxicab distance from P to Q"
+    (+ (abs (- (car p) (car q)))
+       (abs (- (cadr p) (cadr q)))))
+#+end_src

p20/p20.org

@@ -34,23 +34,9 @@ Load map
     (car (advent/coordinates-of ?S data-chars)))
 #+end_src
 
-Define some aux functions
+Let the stack burn
 #+begin_src emacs-lisp :results none
   (setq max-lisp-eval-depth 1000000) ; burn baby burn
-
-  (defun dot (a b)
-    "Return the dot product of the two vectors"
-    (-reduce #'+ (-map (lambda (x) (* (car x) (cdr x))) (-zip-pair a b))))
-
-  (defun neighbour (p dir)
-    "Returns the neighbour to P in the direction DIR"
-    (list (+ (car p) (car dir))
-          (+ (cadr p) (cadr dir))))
-
-  (defun taxicab-distance (p q)
-    "Returns the taxicab distance from P to Q"
-    (+ (abs (- (car p) (car q)))
-       (abs (- (cadr p) (cadr q)))))
 #+end_src
 
 First, we explore the maze and record the path from START to END
@@ -59,10 +45,10 @@ First, we explore the maze and record the path from START to END
     "Explore the maze starting at position P and in the direction
   DIR. Returns a list of positions traversed END to START"
     (if (eq (thing-at p) 'end) (cons p past)
-      (let* ((forward-dirs (--filter (>= (dot it dir) 0)
+      (let* ((forward-dirs (--filter (>= (advent/dot it dir) 0)
                                      '((0 1) (0 -1) (-1 0) (1 0))))
-             (new-dir (car (--filter (not (eq (thing-at (neighbour p it)) 'wall)) forward-dirs))))
-        (explore (neighbour p new-dir) new-dir (cons p past)))))
+             (new-dir (car (--filter (not (eq (thing-at (advent/neighbour  p it)) 'wall)) forward-dirs))))
+        (explore (advent/neighbour  p new-dir) new-dir (cons p past)))))
 
   (setq distance-alist (-map-indexed (lambda (x y) (cons y x))
                                      (explore (starting-pos) '(0 0))))
@@ -77,7 +63,7 @@ Now look for gaps:
    (--filter (>= it 100)
              (--map (- it 2)
                     (-flatten (-non-nil (--map (-non-nil
-                                                (-map (lambda (dir) (subtract-nil (cdr (assoc (neighbour (car it) dir) distance-alist)) (cdr it)))
+                                                (-map (lambda (dir) (subtract-nil (cdr (assoc (advent/neighbour  (car it) dir) distance-alist)) (cdr it)))
                                                                '((0 2) (0 -2) (2 0) (-2 0))))
                                                         distance-alist))))))
 
@@ -95,7 +81,7 @@ then compute the time saved by using the cheat
              (-flatten
               (-map (lambda (x) (--map (- (cdar it) (cdr x) (cdr it))
                                        (--filter (<= (cdr it) 20)
-                                                 (--map (cons it (taxicab-distance (car it) (car x))) distance-alist))))
+                                                 (--map (cons it (advent/taxicab-distance (car it) (car x))) distance-alist))))
                     distance-alist))))
 #+end_src