Day 6, Part 2

advent-of-code.org

@@ -3086,4 +3086,90 @@ After following the instructions, how many lights are lit?
 #+RESULTS[2e528f53a45a3c7e0dcc549d5ac69918287ddd6e]:
 : 377891
 
+** Part 2
+
+You just finish implementing your winning light pattern when you
+realize you mistranslated Santa's message from Ancient Nordic Elvish.
+
+The light grid you bought actually has individual brightness controls;
+each light can have a brightness of zero or more. The lights all start
+at zero.
+
+The phrase =turn on= actually means that you should increase the
+brightness of those lights by =1=.
+
+The phrase =turn off= actually means that you should decrease the
+brightness of those lights by =1=, to a minimum of zero.
+
+The phrase =toggle= actually means that you should increase the
+brightness of those lights by =2=.
+
+What is the total brightness of all lights combined after following
+Santa's instructions?
+
+For example:
+
+- =turn on 0,0 through 0,0= would increase the total brightness by
+  =1=.
+- =toggle 0,0 through 999,999= would increase the total brightness by
+  =2000000=.
+
+----------------------------------------------------------------------
+
+#+BEGIN_SRC emacs-lisp :var input=6-input :exports both
+  (defun day6.2/make-light ()
+    0)
+
+  (defun day6.2/turn-on-light (light)
+    (+ 1 light))
+
+  (defun day6.2/turn-off-light (light)
+    (if (>= 0 light) 0
+      (- light 1)))
+
+  (defun day6.2/toggle-light (light)
+    (+ 2 light))
+
+  (defun day6.2/parse-instruction (instruction)
+    (if (string-match (concat "\\(turn \\(on\\|off\\)\\|toggle\\) "
+                              "\\([0-9]+\\),\\([0-9]+\\)"
+                              " through "
+                              "\\([0-9]+\\),\\([0-9]+\\)")
+                      instruction)
+        (list (cond ((string-equal "turn on" (match-string 1 instruction))
+                     #'day6.2/turn-on-light)
+                    ((string-equal "turn off" (match-string 1 instruction))
+                     #'day6.2/turn-off-light)
+                    ((string-equal "toggle" (match-string 1 instruction))
+                     #'day6.2/toggle-light))
+              (string-to-int (match-string 3 instruction))
+              (string-to-int (match-string 4 instruction))
+              (string-to-int (match-string 5 instruction))
+              (string-to-int (match-string 6 instruction)))))
+
+  (defun day6.2/run-instruction (grid instruction)
+    (let ((parsed-instruction (day6.2/parse-instruction instruction)))
+      (eval (append '(day6/change-range grid)
+                    `(',(first parsed-instruction))
+                    (rest parsed-instruction)))))
+
+  (defun day6.2/make-grid (size)
+    (let ((table (make-hash-table :size (* size size))))
+      (-each (number-sequence 0 (- (* size size) 1))
+        (lambda (pos) (puthash pos (day6.2/make-light) table)))
+      (cons size
+            table)))
+
+  (defun day6.2/total-brightness (grid)
+    (-reduce #'+
+             (day6/grid-lights grid)))
+
+  (let ((grid (day6.2/make-grid 1000)))
+    (-each (split-string input "\n" t)
+      (apply-partially 'day6.2/run-instruction grid))
+    (day6.2/total-brightness grid))
+#+END_SRC
+
+#+RESULTS[ceaf378dab9cbe4211307b258b4fe66d2a04482b]:
+: 14110788