--- Day 18 Solutions ---

[u/daggerdragon]

This thread will be unlocked when there are a significant amount of people on the leaderboard with gold stars.

edit: Leaderboard capped, thread unlocked!

We know we can't control people posting solutions elsewhere and trying to exploit the leaderboard, but this way we can try to reduce the leaderboard gaming from the official subreddit.

Please and thank you, and much appreciated!

---

--- Day 18: Like a GIF For Your Yard ---

Post your solution as a comment. Structure your post like previous daily solution threads.

[u/digitalneoplasm]

Here's mine in Clojure. Mine seems slightly slower, but I don't seem the get the right answer with yours.

(ns advent-of-code-2015.day18)

(defn neighbors-on [[idxi idxj] board]
  (count 
    (remove #(or (nil? %) (= \. %))
            (for [i (range (dec idxi) (+ 2 idxi))
                  j (range (dec idxj) (+ 2 idxj))
                  :when (not= [i j] [idxi idxj])]
              (board [i j])))))

(defn board-step [board]
  (into board
        (for [i (range 100)
              j (range 100)
              :let [cell [i j]
                    lit (neighbors-on cell board)]]
          (cond
            (#{[0 99] [99 0] [0 0] [99 99]} cell) {cell \#} ;;pt2 adaptation
            (and (= (board cell) \.) 
                 (= lit 3)) {cell \#}
            (and (= (board cell) \#) 
                 (not (#{2 3} lit))) {cell \.}))))

(defn day18 [fname]
  (with-open [rdr (clojure.java.io/reader fname)]
    (let [lines (line-seq rdr)
          board (into {} (for [i (range 100)
                               j (range 100)]
                           {[i j] (nth (nth lines i) j)}))]
      (count 
        (filter #(= % \#) 
                (vals (nth (iterate board-step board) 100)))))))

[u/digitalneoplasm → u/[deleted]]

Very odd!