marsrover.clj

(ns marsrover.core
  (:require [clojure.string :as s]))

(defn add-tuple [fst snd]
  [(+ (first fst) (first snd)) (+ (second fst) (second snd))])

(defn input->rovers [input]
  (partition 2 (drop 1 (s/split-lines input))))

(defn next-movement [facing]
  ({"E" [1 0] "W" [-1 0] "N" [0 1] "S" [0 -1]} facing))

(defn rover-map [string]
  (let [pos (s/split string #"\s")]
    {:position [(read-string (first pos)) (read-string (second pos))]
     :next     (next-movement (last pos))}))

(defmulti move (fn [rover command] command))

(defmethod move \M [rover command]
  (assoc rover :position (add-tuple (:position rover) (:next rover))))

(defmethod move \L [rover command]
  (assoc rover :next [(- (second (:next rover))) (first (:next rover))]))

(defmethod move \R [rover command]
  (assoc rover :next [(second (:next rover)) (- (first (:next rover)))]))

(defn main [input]
  (map #(reduce move (rover-map (first %)) (second %)) (input->rovers input)))