aoc2020-23

demo.clj

(ns aoc2020.demo)

(def demo  [3 8 9 1 2 5 4 6 7])

;;transcribed from https://www.youtube.com/watch?v=5AqX3Wu00ok

(defn cups->circle ^longs [cups-prefix ^long total-cups]
  (let [circle (long-array (inc total-cups))]
    (doseq [[a b] (partition 2 1 cups-prefix)]
      (aset-long circle a b))
    (loop [a (last cups-prefix)
           b (inc (count cups-prefix))]
      (if (<= b total-cups)
        (do (aset-long circle a b)
            (recur b (inc b)))
        (aset-long circle a (first cups-prefix))))
    circle))

(defn destination [^longs circle ^long current ^long x ^long y]
  (let [destination (dec (if (= 1 current) (long (alength circle)) current))]
    (if (or (= x destination)
            (= y destination)
            (= (aget circle y) destination))
      (recur circle destination x y)
      destination)))

(defn play-crab-cups [^longs circle ^long current ^long steps]
  (if (zero? steps)
    circle
    (let [x (aget circle current)
          y (aget circle x)
          z (aget circle y)
          next (aget circle z)
          destination (destination circle current x y)]
      (aset-long circle current next)
      (aset-long circle z (aget circle destination))
      (aset-long circle destination x)
      (recur circle next (dec steps)))))


(defn traverse [^longs circle]
  (->> (aget circle 1)
       (iterate (partial aget circle))
       (take 8)
       clojure.string/join))

(defn play [xs current length steps]
  (let [circle (cups->circle xs length)]
    (play-crab-cups circle current steps)
    (traverse circle)))

(defn test-games [n]
  (for [i (range 10)] (play demo 1 9 i)))

(def move-states
  [[3 8 9 1 2 5 4 6 7]
   [3 2 8  9  1  5  4  6  7]
   [3  2 5 4  6  7  8  9  1]
   [7  2  5 8 9  1  3  4  6]
   [3  2  5  8 4 6  7  9  1]
   [9  2  5  8  4 1 3  6  7]
   [7  2  5  8  4  1 9 3  6]
   [8  3  6  7  4  1  9 2 5]
   [7  4  1  5  8  3  9  2 6]
   [5 7  4  1  8  3  9  2  6]
   [5 8 3  7  4  1  9  2  6 ]])

(def moves (mapv #(traverse (cups->circle % 9)) move-states))

;; aoc2020.demo> (map vector moves (test-games 10))
;; (["25467389" "25467389"]
;;  ["54673289" "67389254"]
;;  ["32546789" "69257384"]
;;  ["34672589" "69382574"]
;;  ["32584679" "82569374"]
;;  ["36792584" "89372564"]
;;  ["93672584" "56489372"]
;;  ["92583674" "89564372"]
;;  ["58392674" "84379562"]
;;  ["83926574" "84562379"])


(def move10 "92658374")
(def move100 "67384529")