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diff --git a/year2021/day9/part2.clj b/year2021/day9/part2.clj
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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)
+     )
+