day12.clj

README.md

@@ -48,7 +48,7 @@ Day 00: Helper file                           | [aoc.clj](clojure/aoc.clj)     |
 [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) | Off-by-one trap!
-<!-- [Day 12](http://adventofcode.com/2023/day/12) | [day12.clj](clojure/day12.clj) | -->
+[Day 12](http://adventofcode.com/2023/day/12) | [day12.clj](clojure/day12.clj) | Immutability, meet my friend `atom`.
 <!-- [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) | -->
 <!-- [Day 15](http://adventofcode.com/2023/day/15) | [day15.clj](clojure/day15.clj) | -->

clojure/day12.clj

@@ -0,0 +1,55 @@
+(ns day12
+  (:require aoc
+            [clojure.string :as str]))
+
+
+(def cache (atom {}))
+
+(def is-operational? #{\. \?})
+(def is-damaged? #{\# \?})
+
+
+(defn parse-line [line]
+  (let [[pattern groups] (str/split line #" ")]
+    [pattern (aoc/integers groups)]))
+
+(defn unfold [[patts groups]]
+  [(->> patts
+        (repeat 5)
+        (interpose "?")
+        (apply str))
+   (->> groups
+        (repeat 5)
+        flatten)])
+
+
+(defn arrangements [[pattern groups :as pg]]
+  (if-let [res (@cache pg)]
+    res
+    (if (empty? groups)
+      (if (every? is-operational? pattern) 1 0)
+      (let [[size & tl] groups
+            post (+ (reduce + tl) (count tl))
+            score (atom 0)]
+        (doseq [pre (range (inc (- (count pattern) post size)))
+                :let [[before pattern'] (split-at pre pattern)
+                      [current remaining] (split-at size pattern')]
+                :while (every? is-operational? before)
+                :when (every? is-damaged? current)]
+          (cond
+            (empty? tl) (when (every? is-operational? remaining)
+                          (swap! score inc))
+            (is-operational? (first remaining))
+            (swap! score + (arrangements [(rest remaining) tl]))))
+        (swap! cache assoc pg @score)
+        @score))))
+
+
+(defn solve [input-file]
+  (let [lines (aoc/read-input input-file parse-line)
+        unfolded (map unfold lines)]
+    [(reduce + (map arrangements lines))
+     (reduce + (pmap arrangements unfolded))]))
+
+
+(solve 12)

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?]]))
@@ -35,6 +35,7 @@
 (check-day 9 [114 2] [1581679977 889])
 (check-day 10 [70 8] [6864 349])
 (check-day 11 [374 82000210] [9724940 569052586852])
+(check-day 12 [21 525152] [7286 25470469710341])
 
 (let [summary (run-tests)]
   (when-not (successful? summary)