src/adventofcode2019/day06.clj

   1 (ns adventofcode2019.day06
   2     [:require [adventofcode2019.lib :refer :all]
   3               [clojure.string :as str]])
   4
   5 (defn a-orbits-b [orbits-map [b a]]
   6   (if (contains? orbits-map b)
   7     (-> (assoc orbits-map a {:parent b, :children (get-in orbits-map [a :children] [])})
   8         (update-in [b :children] conj a))
   9     (-> (assoc orbits-map b {:parent nil, :children []})
  10         (a-orbits-b [b a]))))
  11
  12 (defn distances-from [tree node]
  13   (letfn [(path-rc [dist tree node]
  14             (let [seen? #(some? (get-in tree [% :dist]))
  15                   neighbors (remove (some-fn nil? seen?)
  16                                     (cons (get-in tree [node :parent])
  17                                           (get-in tree [node :children])))]
  18               (as-> tree it
  19                     (assoc-in it [node :dist] dist)
  20                     (reduce #(path-rc (inc dist) %1 %2) it neighbors))))]
  21     (path-rc 0 tree node)))
  22
  23 (defn assign-depth [tree]
  24   (let [is-root? #(nil? (get-in tree [% :parent]))
  25         root (first (filter is-root? (keys tree)))]
  26     (letfn [(depth-rc [depth tree root]
  27               (as-> tree it
  28                     (assoc-in it [root :depth] depth)
  29                     (reduce #(depth-rc (inc depth) %1 %2)
  30                             it (get-in tree [root :children]))))]
  31       (depth-rc 0 tree root))))
  32
  33 (defn day06 []
  34   (let [input (map #(str/split % #"\)") (get-list-from-file (input-file)))
  35         orbits-map (reduce a-orbits-b {} input)
  36         with-depths (assign-depth orbits-map)]
  37     (part1 (reduce + (map :depth (vals with-depths))))
  38     (part2 (- (get-in (distances-from orbits-map "YOU") ["SAN" :dist]) 2))))