Add correct day3pt2 solution

[adventofcode2019.git] / src / adventofcode2019 / day03.clj

(ns adventofcode2019.day03
    [:require [adventofcode2019.lib :refer :all]
              [clojure.string :as str]
              [clojure.set :as set]
              [clojure.math.combinatorics :as combo]])

(defn parse-input [input]
  (map #(str/split % #",") (str/split-lines (str/trim (slurp input)))))

(defn spec->op [spec]
  (let [direction (first spec)
        distance (parse-int (str/join (rest spec)))]
    (case direction
      \U (fn [[x y]] [x (+ y distance)])
      \D (fn [[x y]] [x (- y distance)])
      \R (fn [[x y]] [(+ x distance) y])
      \L (fn [[x y]] [(- x distance) y]))))


(defn ints-between [x y]
  (cond 
    (> x y) (reverse (range y (inc x)))
    (< x y) (range x (inc y))
    :else [x]))

(defn points-diff [pos-a pos-b]
  (let [[a-x a-y] pos-a
        [b-x b-y] pos-b]
    (rest (for [x (ints-between a-x b-x)
                y (ints-between a-y b-y)]
               [x y]))))

(defn wire-spec->points [wire]
  (let [wire-ops (map spec->op wire)
        trace-reduction (fn [{:keys [pos points]} op]
                            (let [new-pos (op pos)
                                  new-points (points-diff pos new-pos)]
                              {:pos new-pos :points (concat points new-points)}))
        trace (reduce trace-reduction {:pos [0 0], :points []} wire-ops)]
    (:points trace)))

(defn find-intersections [wires]
  (let [wires-points (map wire-spec->points wires)
        intersections (apply set/intersection (map set wires-points))
        find-steps (fn [i pos] (when (intersections pos) {pos (inc i)}))
        step-counts (map #(map-indexed find-steps %) wires-points)]
    (apply (partial merge-with +) (flatten step-counts))))

(defn day03 []
  (let [wires (parse-input (input-file))
        manhattan-distance (fn [[x y]] (+ (Math/abs x) (Math/abs y)))
        intersections (find-intersections wires)] 
    (println (apply min (map manhattan-distance (keys intersections))))
    (println (apply min (vals intersections)))))