day9.lg

(ns day9)

(def dirs {"U" [0 -1] "D" [0 1] "R" [1 0] "L" [-1 0]})
(def data (->> "input/day9.txt" slurp lines
               (mapcat #(let [[d n] (split % " ")] (repeat (parse-long n) (dirs d))))
               (reductions #(mapv + %1 %2) [0 0])))

(defn next-pos [[tx ty] [hx hy]]
  (let [sign (fn [x] (cond (zero? x) x (< x 0) -1 :else 1))]
    (if (or (-> tx (- hx) abs (> 1)) (-> ty (- hy) abs (> 1))) 
      [(+ tx (sign (- hx tx))) (+ ty (sign (- hy ty)))]
      [tx ty])))

(let [paths (iterate (partial reductions next-pos) data)]
  (println "1:" (->> paths second (map str) set count))
  (println "2:" (->> (nth paths 9) (map str) set count)))