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(require '[clojure.set])
(defn get-adj
"Gets vector of coords surrounding (x, y)."
[y x] [[(dec y) x] [(inc y) x] [y (dec x)] [y (inc x)]])
(defn basin-continues?
"Determines if `b` is a continuation of the basin that includes `a`."
[a b] (and (some? b) (not= b 9) (> b a)))
(defn basin-bottom?
"Determines if point `p` in `hmap` is the bottom of a basin surrounded by
points `adj`."
[hmap p adj]
(every?
#(let [q (get-in hmap %)] (or (nil? q) (< (get-in hmap p) q)))
adj
))
(defn find-basin
"If point `yx` in `hmap` is in a basin (determined using `adj`), return a
list of points in the basin that are above `yx`."
[hmap yx adj]
(let [res (filter #(basin-continues? (get-in hmap yx)
(get-in hmap %))
adj)]
(apply (partial clojure.set/union res)
(map #(set (find-basin hmap % (apply get-adj %))) res)
)))
(->> (slurp "./in")
(clojure.string/split-lines)
(mapv vec)
(mapv (partial mapv #(- (int %) 48)))
(#(for [y (range 0 (count %))
x (range 0 (count (first %)))
:let [adj (get-adj y x)]
:when (basin-bottom? % [y x] adj)]
(inc (count (find-basin % [y x] adj)))))
(sort >)
(take 3)
(apply *)
(println)
)
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