advent-6.clj

(defn parse-int [s]
  (Integer/parseInt s))

(defn parse [inst]
  (let [[_ cmd sx sy ex ey] (re-find #"(turn on|turn off|toggle) (\d+),(\d+) through (\d+),(\d+)" inst)
        sx (parse-int sx)
        sy (parse-int sy)
        ex (parse-int ex)
        ey (parse-int ey)]
    [cmd [sx sy] [ex ey]]))

(defn update-board [board command coords]
  (let [f (condp = command
            "turn on" (fn [b c] (assoc-in b c true))
            "turn off" (fn [b c] (assoc-in b c false))
            "toggle" (fn [b c] (update-in b c not)))]
    (reduce f board coords)))


(->> (let [n 1000
           board (vec (repeat n (vec (repeat n false))))]
       (reduce (fn [b line] (let [[cmd s e] (parse line)]
                              (update-board b cmd (get-coords s e))))
               board
               (str/split-lines (slurp "a6.txt"))))
     flatten
     (filter identity)
     count)