day 18, part 2, not complete, before going ugly

day18.lisp

@@ -11,9 +11,9 @@
 (defun find-maxes (all-coords)
  (loop
   for (x y z) in all-coords
-  maximize (1+ x) into xs
-  maximize (1+ y) into ys
-  maximize (1+ z) into zs
+  maximize (+ x 2) into xs
+  maximize (+ y 2) into ys
+  maximize (+ z 2) into zs
   finally (return (list xs ys zs))) )
 
 (defun fill-connectivity-array (all-coords connectivity-matrix)
@@ -21,7 +21,8 @@
     for (x y z) in all-coords
     do (setf (aref connectivity-matrix x y z) 1)))
 
-(defun neighbors-for (coords connectivity-matrix)
+;; 1 - rock, 0 - initial empty, 2 - outside air
+(defun neighbors-for (coords connectivity-matrix &key (type 1))
   (labels ((coords-fit (potential-point)
              (loop for i from 0 to 2
                    always (and (< (nth i potential-point)
@@ -34,7 +35,7 @@
       for neighbor = (mapcar #'+ coords deltas)
       when
       (and (coords-fit neighbor)
-           (= 1 (apply #'aref connectivity-matrix neighbor)))
+           (= type (apply #'aref connectivity-matrix neighbor)))
       collect neighbor)))
 
 (defun count-open-sides (connectivity-matrix)
@@ -46,3 +47,25 @@
                       when (= 1 (aref connectivity-matrix x y z))
                       summing (- 6
                       (length (neighbors-for (list x y z) connectivity-matrix))))))))
+
+(defun point-at-is (coords connectivity-matrix elem)
+  (= elem (apply #'aref connectivity-matrix coords)))
+
+;; call with initial coord '(0 0 0)
+(defun fill-outside-with-2 (coord connectivity-matrix)
+  (when (point-at-is coord connectivity-matrix 0)
+    (setf (apply #'aref connectivity-matrix coord) 2)
+    (mapcar (lambda (neighbor) (fill-outside-with-2 neighbor connectivity-matrix))
+            (neighbors-for coord connectivity-matrix :type 0))))
+
+(defun count-open-sides-to-outside (connectivity-matrix)
+  (destructuring-bind (n m k)
+      (array-dimensions connectivity-matrix)
+    (loop for x from 0 below n sum
+          (loop for y from 0 below m sum
+                (loop for z from 0 below k
+                      when (= 1 (aref connectivity-matrix x y z))
+                      summing (length (neighbors-for
+                                       (list x y z)
+                                       connectivity-matrix
+                                       :type 2)))))))