06.clj

(ns universal-orbit-map
  (:require [clojure.string :as str]
            [clojure.set]))

;;; part 1
(def orbit-map (->> (slurp "06.in")
                    (str/split-lines)
                    (map (fn [s] (map keyword (str/split s #"\)"))))
                    (reduce (fn [m [orbited orbits]] (assoc m orbits orbited)) {})))

(defn orbits-number [m object]
  (loop [object object, number 0]
    (if (object m)
      (recur (object m) (inc number))
      number)))

(let [objects (set (keys orbit-map))]
  (apply + (map (partial orbits-number orbit-map) objects)))

;;; part 2
(- (count (filter (fn [[object freq]] (= 1 freq))
                  (frequencies (concat (take-while #(not= :COM %) (iterate orbit-map :YOU))
                                       (take-while #(not= :COM %) (iterate orbit-map :SAN))))))
   2)