advent-22-15

(defn calc-dist [[x y] [a b]]
  (+ (abs (- x a)) (abs (- y b))))

(defn manhattan-spread [[[sensorx sensory :as sensor] beacon] line]
  (let [width (- (calc-dist sensor beacon) (abs (- line sensory)))]
    (if
      (neg? width) []
      [(- sensorx width) (+ sensorx width)])))

(defn calc-uncovered [[a b] [c d]]
  (cond
    (< b c) (+ 1 (- d c))
    (= b c) (- d c)
    (< b d) (- d b)
    :else 0))

(defn find-total [y pairs]
  (reduce
    (fn [[total old undetected] spread]
      (let [increase (calc-uncovered (peek old) spread)]
        [(+ total increase) (if (zero? increase) old (conj old spread))]))
    [0 [[Long/MIN_VALUE Long/MIN_VALUE]]]
    (->> pairs
         (map #(manhattan-spread % y))
         (remove empty?)
         (sort-by first))))

(defn find-spots [y pairs coords]
  (- (first (find-total y pairs)) (->> coords (map second) (filter #(= y %)) count)))

(defn find-gaps [y pairs minx maxx] (let [covers (second (find-total y pairs))]
  (reduce
    (fn [[res [a b :as latest]] [c d :as current]]
      (cond
        res [res current]
        (and (>= b minx) (<= c maxx) (< b (dec c))) [[(inc b) y] current]
        :else [nil current]))
    [nil (first covers)]
    (rest covers))))

(with-open [rdr (clojure.java.io/reader "sensors.in")]
  (let [
    coords (->> rdr
                line-seq
                (map #(clojure.string/split % #"="))
                flatten
                (map #(clojure.string/split % #" "))
                flatten
                (map #(clojure.string/replace % #"[^0-9-]" ""))
                (remove clojure.string/blank?)
                (map #(Integer/parseInt %))
                (partition 2))
    pairs (partition 2 coords)
    coords (set (map vec coords))]
    (println (find-spots 2000000 pairs coords))
    (->>
      (range 4000000)
      (map #(find-gaps % pairs 0 4000000))
      (map first)
      (filter some?)
      first
      ((fn [[x y]] (+ y (* 4000000 x))))
      println)
))