aoc_2021_3.clj

(defn part-1 [input]
  (->> input
       str/split-lines
       (map seq)
       (apply map list)
       (map #(vals (into (sorted-map) (set/map-invert (frequencies %)))))
       (apply map list)
       (map (comp #(Integer/parseInt % 2) str/join))
       (apply *)))

(defn get-rating [input idx n]
  (let [fbits (nth (apply mapv list input) n)
        m (frequencies fbits)
        m (cond
            (not (get m \0)) (assoc m \0 0)
            (not (get m \1)) (assoc m \1 1)
            :else m)
        v (vals (into (sorted-map) (set/map-invert m)))
        x (cond
            (and (= 1 (count v)) (= 0 idx)) \0
            (and (= 1 (count v)) (= 1 idx)) \1
            :else (nth v idx))
        input-next (filter #(= x (nth % n)) input)]
    (if (= 1 (count input-next))
      (-> (first input-next) str/join (Integer/parseInt 2))
      (recur input-next idx (inc n)))))

(defn part-2 [input]
  (let [parsed-input (->> input str/split-lines (map (comp vec seq)))]
    (* (get-rating parsed-input 0 0)
       (get-rating parsed-input 1 0))))