Day 8, Part 2

advent-of-code.org

@@ -4108,3 +4108,59 @@ number of characters in memory for string values =(0 + 3 + 7 + 1 =
 #+RESULTS[acaa7a9432ace3b411d0bfcd4c61620b43ce21c5]:
 : 1350
 
+** Part 2
+Now, let's go the other way. In addition to finding the number of
+characters of code, you should now *encode each code representation as
+a new string* and find the number of characters of the new encoded
+representation, including the surrounding double quotes.
+
+For example:
+
+- =""= encodes to ="\"\""=, an increase from =2= characters to =6=.
+- ="abc"= encodes to ="\"abc\""=, an increase from =5= characters to
+  =9=.
+- ="aaa\"aaa"= encodes to ="\"aaa\\\"aaa\""=, an increase from =10=
+  characters to =16=.
+- ="\x27"= encodes to ="\"\\x27\""=, an increase from =6= characters
+  to =11=.
+
+Your task is to find *the total number of characters to represent the
+newly encoded strings* minus *the number of characters of code in each
+original string literal*. For example, for the strings above, the
+total encoded length (=6 + 9 + 16 + 11 = 42=) minus the characters in
+the original code representation (=23=, just like in the first part of
+this puzzle) is =42 - 23 = 19=.
+
+----------------------------------------------------------------------
+
+#+BEGIN_SRC emacs-lisp :var input=8-input :exports both
+  (defun day8/encode-string (string-literal)
+    (format "\"%s\""
+            (-reduce-from
+             (lambda (acc replacement)
+               (s-replace (car replacement)
+                          (cdr replacement)
+                          acc))
+             string-literal
+             '(("\\" . "\\\\")
+               ("\"" . "\\\"")))))
+
+  (ert-deftest day8/encode-string ()
+    (should (string-equal "\"\\\"\\\"\""
+                          (day8/encode-string "\"\"")))
+    (should (string-equal "\"\\\"abc\\\"\""
+                          (day8/encode-string "\"abc\"")))
+    (should (string-equal "\"\\\"aaa\\\\\\\"aaa\\\"\""
+                          (day8/encode-string "\"aaa\\\"aaa\"")))
+    (should (string-equal "\"\\\"\\\\x27\\\"\""
+                          (day8/encode-string "\"\\x27\""))))
+
+  (let* ((code-strings (split-string input "\n" t))
+         (encoded-values (-map #'day8/encode-string code-strings)))
+    (- (-sum (-map #'length encoded-values))
+       (-sum (-map #'length code-strings))))
+#+END_SRC
+
+#+RESULTS[bb50e3c25f6d0d1247acdefae2e5c755c90fe7a7]:
+: 2085
+