2 files changed, 83 insertions(+), 0 deletions(-)

A day11.lisp
A input/day11.txt

@@ 0,0 1,73 @@
+(defpackage #:advent2021.day11
+  (:use #:cl #:alexandria #:cl-ppcre #:advent2021.util)
+  (:export #:solve-part-1 #:solve-part-2))
+
+(in-package #:advent2021.day11)
+
+
+
+(defparameter +input+
+  (loop :with lines := (parse-lines #'identity)
+        :with array := (make-array (list (length lines) (length (first lines))))
+        :for line :in lines
+        :for y :upfrom 0
+        :do (loop :for c :across line
+                  :for x :upfrom 0
+                  :do (setf (aref array y x) (- (char-code c)
+                                                (char-code #\0))))
+        :finally (return array)))
+
+
+(defparameter +width+ (array-dimension +input+ 1))
+(defparameter +height+ (array-dimension +input+ 0))
+
+(defun tick (grid x y touch-array)
+  (when (or (< x 0)
+            (< y 0)
+            (>= x +width+)
+            (>= y +height+)
+            (= 1 (aref touch-array y x)))
+    (return-from tick))
+  (incf (aref grid y x))
+  (when (> (aref grid y x) 9)
+    (setf (aref touch-array y x) 1)
+    (tick grid (1- x) (1- y) touch-array)
+    (tick grid (1- x) y touch-array)
+    (tick grid (1- x) (1+ y) touch-array)
+    (tick grid x (1- y) touch-array)
+    (tick grid x (1+ y) touch-array)
+    (tick grid (1+ x) (1- y) touch-array)
+    (tick grid (1+ x) y touch-array)
+    (tick grid (1+ x) (1+ y) touch-array)))
+
+(defun tick-all (grid touch-array)
+  (loop :for x :below +width+
+        :do (loop :for y :below +height+
+                  :do (tick grid x y touch-array))))
+
+(defun clear-touches (grid touch-array)
+  (loop :for x :below +width+
+        :sum (loop :for y :below +height+
+                   :count (when (= 1 (aref touch-array y x))
+                            (setf (aref grid y x) 0)
+                            (setf (aref touch-array y x) 0)
+                            t))))
+
+(defun solve-part-1 ()
+  (loop :with grid := (copy-array +input+)
+        :with touch-array := (make-array (list +height+ +width+)
+                                         :element-type 'bit)
+        :with flashes := 0
+        :repeat 100
+        :do (tick-all grid touch-array)
+            (incf flashes (clear-touches grid touch-array))
+        :finally (Return flashes)))
+
+(defun solve-part-2 ()
+  (loop :with grid := (copy-array +input+)
+        :with touch-array := (make-array (list +height+ +width+)
+                                         :element-type 'bit)
+        :for generations :upfrom 1
+        :do (tick-all grid touch-array)
+        :until (= (clear-touches grid touch-array) (* +width+ +height+))
+          :finally (return generations)))

@@ 0,0 1,10 @@
+8577245547
+1654333653
+5365633785
+1333243226
+4272385165
+5688328432
+3175634254
+6775142227
+6152721415
+2678227325