day11.clj

README.md

@@ -47,7 +47,7 @@ Day 00: Helper file                           | [aoc.clj](clojure/aoc.clj)     |
 [Day 08](http://adventofcode.com/2023/day/8)  | [day08.clj](clojure/day08.clj) | Underwhelming to see _that_ to be solution for part 2.
 [Day 09](http://adventofcode.com/2023/day/9)  | [day09.clj](clojure/day09.clj) | .esreveR
 [Day 10](http://adventofcode.com/2023/day/10) | [day10.clj](clojure/day10.clj) | No BFS needed.
-<!-- [Day 11](http://adventofcode.com/2023/day/11) | [day11.clj](clojure/day11.clj) | -->
+[Day 11](http://adventofcode.com/2023/day/11) | [day11.clj](clojure/day11.clj) | Off-by-one trap!
 <!-- [Day 12](http://adventofcode.com/2023/day/12) | [day12.clj](clojure/day12.clj) | -->
 <!-- [Day 13](http://adventofcode.com/2023/day/13) | [day13.clj](clojure/day13.clj) | -->
 <!-- [Day 14](http://adventofcode.com/2023/day/14) | [day14.clj](clojure/day14.clj) | -->

clojure/aoc.clj

@@ -114,7 +114,7 @@
         false
         (recur (dec idx) acc)))))
 
-(defn count-if [pred xs]
+(defn count-if ^long [pred xs]
   (reduce
    (fn [^long acc x]
      (if (pred x) (inc acc) acc))

clojure/day11.clj

@@ -0,0 +1,43 @@
+(ns day11
+  (:require aoc))
+
+
+(def ^:const multi (dec 1000000))
+
+
+(defn empty-lines [lines]
+  (keep
+   (fn [[i line]]
+     (when (every? #(= % \.) line) i))
+   (map-indexed vector lines)))
+
+(defn expand [universe]
+  (let [empty-rows (empty-lines universe)
+        empty-cols (empty-lines (aoc/transpose universe))]
+    (for [[^long y line] (map-indexed vector universe)
+          [^long x chr]  (map-indexed vector line)
+          :when (= chr \#)
+          :let [move-right (aoc/count-if #(< ^long % x) empty-cols)
+                move-down  (aoc/count-if #(< ^long % y) empty-rows)]]
+      [[(+ x move-right)
+        (+ y move-down)]
+       [(+ x (* multi move-right))
+        (+ y (* multi move-down))]])))
+
+(defn distances [coords]
+  (for [[^long x1 ^long y1] coords
+        [^long x2 ^long y2] coords
+        :while (not (and (= x1 x2) (= y1 y2)))]
+    (+ (- x1 x2) (abs (- y1 y2)))))
+
+(defn solve [input-file]
+  (let [universe (->> (aoc/read-input input-file)
+                      expand
+                      sort)
+        p1-galaxies (map first universe)
+        p2-galaxies (map second universe)]
+    [(reduce + (distances p1-galaxies))
+     (reduce + (distances p2-galaxies))]))
+
+
+(solve 11)

clojure/tests/solutions_tests.clj

@@ -2,7 +2,7 @@
   (:require
    day01 day02 day03 day04 day05
    day06 day07 day08 day09 day10
-   ; day11 day12 day13 day14 day15
+   day11 ; day12 day13 day14 day15
    ; day16 day17 day18 day19 day20
    ; day21 day22 day23 day24 day25
    [clojure.test :refer [deftest is run-tests successful?]]))
@@ -34,7 +34,7 @@
 (check-day 8 nil [11567 9858474970153])
 (check-day 9 [114 2] [1581679977 889])
 (check-day 10 [70 8] [6864 349])
-
+(check-day 11 [374 82000210] [9724940 569052586852])
 
 (let [summary (run-tests)]
   (when-not (successful? summary)