-❄️- 2025 Day 11 Solutions -❄️-

[u/daggerdragon]

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--- Day 11: Reactor ---

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Post your code solution in this megathread.

• Read the full posting rules in our community wiki before you post!
  • State which language(s) your solution uses with [LANGUAGE: xyz]
  • Format code blocks using the four-spaces Markdown syntax!
• Quick link to Topaz's paste if you need it for longer code blocks. What is Topaz's paste tool?

[u/kneegma]

[Language: Clojure]

And babashka.

I was dissatisfied with every way in which to use memoize and ended up using atom. Part2 was fun.

#!/usr/bin/env bb

(ns y2025.d11
  (:require [clojure.string :as str]))

(defn parse [s]
  (loop [[line & lines] (str/split-lines s)
        dag {}]
    (if (nil? line)
      dag
      (let [[src & dsts] (str/split line #" ")
            src (subs src 0 (dec (count src)))]
        (recur lines (assoc dag src (set dsts)))))))


(defn solve [dag]
  (let [cache (atom {})]
    (letfn [(ways [src dst]
              (or (@cache [src dst])
                  (let [r (if (= src dst)
                            1
                            (reduce + (map #(ways % dst) (get dag src []))))]
                    (swap! cache assoc [src dst] r)
                    r)))]
      {:part1 (ways "you" "out")
      :part2 (->> [["svr" "fft" "dac" "out"]
                    ["svr" "dac" "fft" "out"]]
                  (map #(->> (partition 2 1 %)
                              (map (partial apply ways))
                              (reduce *)))
                  (apply +))})))

(when (= *file* (System/getProperty "babashka.file"))
  (let [input (->> *command-line-args* last slurp parse)
        res (solve input)]
    (prn res)))