advent-9.clj

(ns advent.a9
  (:require [clojure.string :as str]
            [clojure.math.combinatorics :refer [permutations]]))

(def text "AlphaCentauri to Snowdin = 66
AlphaCentauri to Tambi = 28
AlphaCentauri to Faerun = 60
AlphaCentauri to Norrath = 34
AlphaCentauri to Straylight = 34
AlphaCentauri to Tristram = 3
AlphaCentauri to Arbre = 108
Snowdin to Tambi = 22
Snowdin to Faerun = 12
Snowdin to Norrath = 91
Snowdin to Straylight = 121
Snowdin to Tristram = 111
Snowdin to Arbre = 71
Tambi to Faerun = 39
Tambi to Norrath = 113
Tambi to Straylight = 130
Tambi to Tristram = 35
Tambi to Arbre = 40
Faerun to Norrath = 63
Faerun to Straylight = 21
Faerun to Tristram = 57
Faerun to Arbre = 83
Norrath to Straylight = 9
Norrath to Tristram = 50
Norrath to Arbre = 60
Straylight to Tristram = 27
Straylight to Arbre = 81
Tristram to Arbre = 90")

(def test "London to Dublin = 464
London to Belfast = 518
Dublin to Belfast = 141")

(defn parse [l]
  (let [[_ from to dist] (re-find #"^(\w+) to (\w+) = (\d+)" l)]
    [from to (Integer/parseInt dist)]))

(defn distmap [dists]
  (reduce (fn [dict [from to dist]]
            (-> dict
                (update from (fn [dests] (assoc dests to dist)))
                (update to (fn [dests] (assoc dests from dist)))))
          {} dists))

(def cities (vec (apply hash-set (flatten (map #(take 2 %) dists)))))

(defn routes [distmap]
  (for [route (permutations (keys distmap))]
    [route (reduce + (for [leg (partition 2 1 route)]
                       (get-in distmap leg)))]))

(let [distances (->> text
                     (str/split-lines)
                     (map parse)
                     distmap
                     routes
                     (map second))]
  [(apply min distances) (apply max distances)])