[p4] Part 1 and 2

I am unhappy with the coding style.

p4/p4.org

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+#+title: Solution to p4
+
+Yay, a maze. Cool.
+No, not cool.
+
+#+begin_src emacs-lisp :results none
+  (with-temp-buffer
+    (insert-file-contents "input")
+    (advent/replace-multiple-regex-buffer
+     '(("^\\(.*\\)$" . "\"\\1\" ")))
+    (goto-char (point-min))
+    (insert "(setq data '(")
+    (goto-char (point-max))
+    (insert "))")
+    (eval-buffer))
+
+  (setq data-char (-map #'advent/split-string-into-char-list data)
+        width (length (car data-char))
+        height (length data-char))
+#+end_src
+
+This is for part 1; easy
+#+begin_src emacs-lisp
+  (defun position-valid-p (pos)
+    (and (and (>= (car pos) 0) (< (car pos) width))
+         (and (>= (cadr pos) 0) (< (cadr pos) height))))
+
+  (defun roll-at-p (pos data-char)
+    (when (position-valid-p pos)
+      (eq ?@ (advent/char-at pos data-char))))
+
+  (setq adjacent '((-1 -1)
+                   (-1 0)
+                   (-1 1)
+                   (0 1)
+                   (0 -1)
+                   (1 -1)
+                   (1 0)
+                   (1 1)))
+
+  (defun rolls-adjacent (pos data-char)
+    (length (-non-nil (--map (roll-at-p it data-char) (--map (advent/neighbour pos it) adjacent)))))
+
+  (length (--filter (< it 4)
+                    (--map (rolls-adjacent it data-char) (advent/coordinates-of ?@ data-char))))
+
+#+end_src
+
+#+RESULTS:
+: 1464
+
+Now for part two, we create a new data-char at each removal step
+I am not particularly happy style-wise, but that is it for today
+#+begin_src emacs-lisp
+  (defun tensor (a b)
+    (-map (lambda (x) (--map (list it x) a)) b))
+
+  (setq initial-roll-number (length (advent/coordinates-of ?@ data-char))
+        current-roll-number (1+ initial-roll-number))
+
+  (while (> current-roll-number
+            (setq current-roll-number (length (advent/coordinates-of ?@ data-char))))
+    (setq data-char
+        (-map (lambda (row)
+           (--map (if (and (= ?@ (advent/char-at it data-char))
+                           (<= 4 (rolls-adjacent it data-char)))
+                      ?@ ?.)
+                  row))
+         (tensor (-iterate #'1+ 0 width)
+                 (-iterate #'1+ 0 height)))))
+
+  (- initial-roll-number current-roll-number)
+#+end_src
+
+#+RESULTS:
+: 8409