advent-22-09

(defn follow [[hx hy] [tx ty]] (let [change {false dec, true inc}] (
  cond
    (every? #{-1 0 1} [(- hx tx) (- hy ty)]) [tx ty]
    (zero? (- hx tx)) [tx ((change (> hy ty)) ty)]
    (zero? (- hy ty)) [((change (> hx tx)) tx) ty]
    :else [((change (> hx tx)) tx) ((change (> hy ty)) ty)]
)))

(defn make-step [dir head tail] (let [
  transforms {"R" [inc identity], "U" [identity inc], "D" [identity dec], "L" [dec identity]}
  transform (transforms dir)
  new-head (vec (map #(%1 %2) transform head))
] [new-head (follow new-head tail)]))

(defn travel [[history knots] [dir steps]] (reduce
  (fn [[history knots] _] (let [
    [head sec] (make-step dir (first knots) (second knots))
    new-knots (reduce #(conj %1 (follow (peek %1) %2)) [sec] (nthrest knots 2))
  ] [(conj history (peek new-knots)) (concat [head] new-knots)]))
  [history knots]
  (range steps)
))

(defn do-task [travel] (
  -> travel first distinct count println
))

(with-open [rdr (clojure.java.io/reader "trail.in")] (
  let [
    lines (->> rdr
      line-seq
      (map #(clojure.string/split % #" "))
      (map (fn [[dir steps]] [dir (Integer/parseInt steps)])))
  ] (->> lines
      (reduce travel [[[0 0]] [[0 0] [0 0]]])
      do-task)
    (->> lines
      (reduce travel [[[0 0]] (vec (replicate 10 [0 0]))])
      do-task)
))