day_06.clj

(ns day_06
  (:require [utils :refer [map-keys map-vals open-resource parse-int split-by-comma]]))

(def input-file "day_06.txt")

(def data (->> input-file open-resource first split-by-comma (map parse-int)))

(defn part-01 [input days]
  (let [merge-overlapping-ages (fn [m]
                                 (merge-with +
                                             (dissoc m -1)
                                             {6 (get m -1 0)
                                              8 (get m -1 0)}))]
    (loop [fish (->> input
                     (group-by identity)
                     (map-vals count))
           day 1]
      (let [updated-fish (->> fish
                              (map-keys dec)
                              merge-overlapping-ages)]
        (if (< day days)
          (recur updated-fish (inc day))
          (->> updated-fish vals (reduce +)))))))

(defn -main [& _]
  (println "Day 06:")
  (println "\t-> Part 1: " (part-01 data 80))
  (println "\t-> Part 2: " (part-01 data 256)))