From 7a62286670ae00a77264054c71723af0f65e234c Mon Sep 17 00:00:00 2001
From: Clyne Sullivan <clyne@bitgloo.com>
Date: Thu, 9 Dec 2021 09:01:17 -0500
Subject: [PATCH] add day 9

---
 day9/part1.clj | 37 +++++++++++++++++++++++++++++
 day9/part2.clj | 64 ++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 101 insertions(+)
 create mode 100644 day9/part1.clj
 create mode 100644 day9/part2.clj

diff --git a/day9/part1.clj b/day9/part1.clj
new file mode 100644
index 0000000..813d5a6
--- /dev/null
+++ b/day9/part1.clj
@@ -0,0 +1,37 @@
+(def input-map
+  (->> (slurp "./in")
+       (clojure.string/split-lines)
+       (mapv vec)
+       (mapv (partial mapv #(- (int %) 48)))
+       ))
+
+(defn compare-heights [a b]
+  (if (or (nil? a) (nil? b) (< a b)) 1 0))
+
+(println
+  (apply +
+      (for [y (range 0 (count input-map))
+            x (range 0 (count (first input-map)))]
+        (let [height (get-in input-map [y x])]
+          (if
+            (= 4
+               (apply +
+                 (map
+                   (partial compare-heights height)
+                   [
+                    (get-in input-map [(dec y) x])
+                    (get-in input-map [(inc y) x])
+                    (get-in input-map [y (dec x)])
+                    (get-in input-map [y (inc x)])
+                   ]
+                   )
+                 )
+               )
+            (inc height)
+            0
+            )
+          )
+        )
+    )
+  )
+
diff --git a/day9/part2.clj b/day9/part2.clj
new file mode 100644
index 0000000..455cb39
--- /dev/null
+++ b/day9/part2.clj
@@ -0,0 +1,64 @@
+(def input-map
+  (->> (slurp "./in")
+       (clojure.string/split-lines)
+       (mapv vec)
+       (mapv (partial mapv #(- (int %) 48)))
+       ))
+
+(defn basin-bottom-single? [a b]
+  (if (or (nil? a) (nil? b) (< a b)) 1 0))
+
+(defn basin-continues? [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 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)
+      []
+      (apply
+        (partial concat res)
+        (map
+          #(find-basin hmap (first %) (second %) (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
+                  ))))))))
+