[p1] better solution

p1/p1.org

@@ -23,31 +23,27 @@ number of 0's mod 100; that is what we need for part 1
 #+RESULTS:
 : 962
 
-For part 2, This ain't pretty, but it works:
+For part 2, This works:
 - we count the number of full turns that have been done in each
-  rotation
-- we add the number of times we landed at 0 by turning left and then
-  right immediately after; these have not been counted above
+  rotation. Since there are corner cases we need to average over two
+  offsets of ½
+
 #+begin_src emacs-lisp
   (defun advent/consecutive-pairs (list)
     (-zip-pair list (cdr list)))
 
-  (let ((number-list (-running-sum (append '(50) data))))
-    (+
-     (-sum (--map (abs (- (car it) (cdr it)))
-                  (advent/consecutive-pairs
-                   (--map (floor it 100) number-list))))
-
-     (length
-      (--filter (and (eq (car it) 0) (< (cdr it) 0))
-                (-zip-pair
-                 (cdr (--map (mod it 100) number-list)) data)))
-
-     (* -1 (length
-            (--filter (and (eq (car it) 0) (< (cdr it) 0))
-                      (-zip-pair
-                       (cdr (--map (mod it 100) number-list)) (cdr data)))))))
+  (defun average (li)
+    (/ (-sum li) (length li)))
+
+  (let ((number-lists (--map (-running-sum (append (list it) data))
+  			   (list 50.5 49.5))))
+    (average (--map 
+  	    (-sum (--map (abs (- (car it) (cdr it)))
+  			 (advent/consecutive-pairs
+  			  (--map (floor it 100) it))))
+  	    number-lists)))
 #+end_src
 
 #+RESULTS:
 : 5782
+