1 files changed, 54 insertions, 0 deletions
diff --git a/day20.clj b/day20.clj
new file mode 100644
index 0000000..017d829
--- /dev/null
+++ b/day20.clj
@@ -0,0 +1,54 @@
+(def tiles
+  (->> (clojure.string/split (slurp "day20") #"\n\n")
+       (map (fn [x]
+              (let [[name & data] (clojure.string/split-lines x)]
+                {(read-string (first (re-seq #"\d+" name)))
+                 (vec data)}
+                )))
+       (into {})))
+
+;; clockwise
+(defn borders [tile]
+  [(first tile)
+   (apply str (reverse (first tile)))
+
+   (apply str (map last tile))
+   (apply str (reverse (map last tile)))
+
+   (last tile)
+   (apply str (reverse (last tile)))
+
+   (apply str (map first tile))
+   (apply str (reverse (map first tile)))
+   ])
+
+(def tile-borders
+  (into {} (for [[k v] tiles] [k (borders v)])))
+
+(def corners
+  (filter
+   (fn [x]
+     (= 2 (count
+           (remove empty?
+                   (for [y (keys tile-borders) :when (not= x y)]
+                     (clojure.set/intersection (set (tile-borders x))
+                                               (set (tile-borders y))))))))
+   (keys tile-borders)))
+
+(apply * corners)  ; => 29584525501199
+
+;; too lazy to do part2, guess it instead:
+
+(defn count-hashes [tile]
+  (->> (rest (butlast tile))
+       (map (comp rest butlast))
+       flatten
+       (filter #{\#})
+       count))
+
+(apply + (map count-hashes (vals tiles))) ;; => 2175
+
+;; grep '#\.\.\.\.##' day20 | wc -l
+;; 41
+
+(- 2175 (* 15 34)) ;; => 1665