From 7b46cd6b6c163e652a9f3ec6aa9ae9299fc7d023 Mon Sep 17 00:00:00 2001
From: Jacopo De Simoi <wilderjds@protonmail.com>
Date: Thu, 11 Sep 2025 10:35:43 -0400
Subject: [PATCH] Add ~coordinates-of~ to library

---
 lib/lib-advent.org | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/lib/lib-advent.org b/lib/lib-advent.org
index 68e7ad8..e4cd225 100644
--- a/lib/lib-advent.org
+++ b/lib/lib-advent.org
@@ -19,3 +19,16 @@
       "Split the string into a list of chars"
       (--map (string-to-char it) (split-string str "\\|.+" t)))
   #+end_src
+
+  #+begin_src emacs-lisp
+    (defun advent/coordinates-of (e li)
+      "This takes a 2D list (a list of lists) of chars LI and an element E
+    and returns a list of positions in LI that contain the element E.
+    "
+      (-map #'cadr
+            (--filter (eq (car it) e)
+                      (-mapcat #'identity
+                               (-map-indexed (lambda (y l)
+                                               (-map-indexed (lambda (x el) (list el (list x y))) l))
+                                             li)))))
+  #+end_src