day19

1 files changed, 40 insertions, 0 deletions

diff --git a/day19.clj b/day19.clj
new file mode 100644
index 0000000..74c78fe
--- /dev/null
+++ b/day19.clj
@@ -0,0 +1,40 @@
+(let [[r m] (clojure.string/split (slurp "day19") #"\n\n")]
+  (def rules (clojure.string/split-lines r))
+  (def messages (clojure.string/split-lines m)))
+
+(def rules
+  (into {}
+        (map (fn [rule]
+               (let [[id r] (clojure.string/split rule #": *")
+                     rs (clojure.string/split r #" *\| *")
+                     rss (map #(clojure.string/split % #" ") rs)
+                     rsp (map (partial map #(case %
+                                              ("\"a\"" "\"b\"") (second %)
+                                              (read-string %))) rss)]
+                 {(read-string id) rsp}))
+             rules)))
+
+(defn lookup [rules id depth]
+  (if (> depth 15)
+    "NEVER"
+    (if (char? id)
+      id
+      (let [v (rules id)]
+        (str "("
+             (clojure.string/join
+              "|"
+              (map (fn [a]
+                     (clojure.string/join
+                      (map #(lookup rules % (inc depth)) a))) v))
+             ")")))))
+
+(let [pattern (re-pattern (lookup rules 0 0))]
+  (count (filter (partial re-matches pattern) messages)))
+;; => 126
+
+(let [rules2 (into rules
+                   [[8  '((42)    (42 8))]
+                    [11 '((42 31) (42 11 31))]])
+      pattern (re-pattern (lookup rules2 0 0))]
+  (count (filter (partial re-matches pattern) messages)))
+;; => 282