day9: document part 2

diff --git a/day9/part2.clj b/day9/part2.clj
index 455cb39655625a239ea81a8fad44bd8b89cf16bc..dd05b7d1a66b9cae73675af7ff9456bcb44c7510 100644 (file)
--- a/day9/part2.clj
+++ b/day9/part2.clj
@@ -5,60 +5,50 @@
        (mapv (partial mapv #(- (int %) 48)))
        ))
 
-(defn basin-bottom-single? [a b]
-  (if (or (nil? a) (nil? b) (< a b)) 1 0))
+(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? [a b]
+(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? [hmap p adj]
-  (= 4
-    (apply +
-      (map
-        #(basin-bottom-single?
-           (get-in hmap p)
-           (get-in hmap %))
-        adj
-        ))))
+(defn basin-bottom?
+  "Determines if point `p` in `hmap` is the bottom of a basin surrounded by
+   points `adj`."
+  [hmap p adj]
+  (empty?
+    (filter
+      #(let [q (get-in hmap %)] (and (some? q) (> (get-in hmap p) q)))
+      adj
+      )))
 
-(defn get-adj [y x]
-  [[(dec y) x]
-   [(inc y) x]
-   [y (dec x)]
-   [y (inc x)]])
-
-(defn find-basin [hmap y x adj]
-  (let [res (reduce
-              #(if
-                   (basin-continues? (get-in hmap [y x])
-                                     (get-in hmap %2))
-                 (conj %1 %2)
-                 %1)
-              []
-              adj
-              )]
-    (if (empty? res)
-      []
+(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)]
+    (if-not (empty? res)
       (apply
         (partial concat res)
         (map
-          #(find-basin hmap (first %) (second %) (apply get-adj %))
-          res))
-      )
-    )
-  )
+          #(find-basin hmap % (apply get-adj %))
+          res
+          )))))
 
-(println
-  (apply *
-    (take 3
-      (sort >
-        (filter
-          pos?
-            (for [y (range 0 (count input-map))
-                   x (range 0 (count (first input-map)))]
-              (let [adj (get-adj y x)]
-                (if (basin-bottom? input-map [y x] adj)
-                  (count (distinct (concat [[y x]] (find-basin input-map y x adj))))
-                  0
-                  ))))))))
+(->> (for [y (range 0 (count input-map))
+           x (range 0 (count (first input-map)))]
+       (let [adj (get-adj y x)]
+         (when (basin-bottom? input-map [y x] adj)
+           (inc (count (distinct (find-basin input-map [y x] adj))))
+           )))
+     (filter some?)
+     (sort >)
+     (take 3)
+     (apply *)
+     (println)
+     )