commit 3485ab4d7bc8df427f64ce0fdf79a9cdb55bccf5
from: Lukas Henkel <lh@entf.net>
date: Mon Dec 11 17:59:41 2023 UTC

Refactor day 11

commit - abba33e8d2bac06e0a3f5057c7e164b078c2b7bb
commit + 3485ab4d7bc8df427f64ce0fdf79a9cdb55bccf5
blob - bde12bd7cfb98deeee747a39bce04ed4bb24584c
blob + 8fabdb84cfd88b54dc810c2db1d14760424f7f62
--- src/day-11.lisp
+++ src/day-11.lisp
@@ -3,8 +3,7 @@
   (:export #:day-11))
 (in-package #:aoc/day-11)
 
-(defun find-galaxies (map &optional (expansion-factor 2))
-  (decf expansion-factor)
+(defun find-galaxies (map)
   (let (galaxies
         empty-rows
         empty-cols)
@@ -20,26 +19,28 @@
           unless (loop for x from 0 below (input-map-width map)
                        thereis (char= (map-cell map (cons x y)) #\#))
             do (push y empty-rows))
-    (loop for galaxy in galaxies
-          collect (cons (+ (point-x galaxy)
-                           (* (count-if (curry #'> (point-x galaxy)) empty-cols)
-                              expansion-factor))
-                        (+ (point-y galaxy)
-                           (* (count-if (curry #'> (point-y galaxy)) empty-rows)
-                              expansion-factor))))))
+    (values galaxies empty-rows empty-cols)))
 
+(defun expand-universe (galaxies empty-rows empty-cols expansion-factor)
+  (decf expansion-factor)
+  (loop for galaxy in galaxies
+        collect (cons (+ (point-x galaxy)
+                         (* (count-if (curry #'> (point-x galaxy)) empty-cols)
+                            expansion-factor))
+                      (+ (point-y galaxy)
+                         (* (count-if (curry #'> (point-y galaxy)) empty-rows)
+                            expansion-factor)))))
+
+(defun sum-distances (galaxies)
+  (loop for (galaxy-1 . rest) on galaxies
+        while rest
+        sum (loop for galaxy-2 in rest
+                  sum (manhattan-distance galaxy-1 galaxy-2))))
+
 (defun day-11 (input)
-  (let* ((map (make-map input))
-         (galaxies-1 (find-galaxies map))
-         (galaxies-2 (find-galaxies map 1000000))
-         (task-1 0)
-         (task-2 0))
-    (map-combinations (lambda (p)
-                        (incf task-1 (apply #'manhattan-distance p)))
-                      galaxies-1
-                      :length 2)
-    (map-combinations (lambda (p)
-                        (incf task-2 (apply #'manhattan-distance p)))
-                      galaxies-2
-                      :length 2)
-    (values task-1 task-2)))
+  (multiple-value-bind (galaxies empty-rows empty-cols)
+      (find-galaxies (make-map input))
+    (let ((galaxies-1 (expand-universe galaxies empty-rows empty-cols 2))
+          (galaxies-2 (expand-universe galaxies empty-rows empty-cols 1000000)))
+      (values (sum-distances galaxies-1)
+              (sum-distances galaxies-2)))))