1 files changed, 67 insertions, 0 deletions
diff --git a/year2021/day16/part1.clj b/year2021/day16/part1.clj
new file mode 100644
index 0000000..2358e59
--- /dev/null
+++ b/year2021/day16/part1.clj
@@ -0,0 +1,67 @@
+(require '[clojure.string :as str])
+(require '[clojure.set :as set])
+
+(def hex-lookup
+  {\0 "0000" \1 "0001" \2 "0010" \3 "0011"
+   \4 "0100" \5 "0101" \6 "0110" \7 "0111"
+   \8 "1000" \9 "1001" \A "1010" \B "1011"
+   \C "1100" \D "1101" \E "1110" \F "1111"})
+
+(defn binary-to-num [binstr]
+  (reduce
+    #(cond-> %1 true (* 2) (= \1 %2) inc)
+    0
+    binstr))
+
+(defn take-packet-version [packet]
+  (-> (split-at 3 packet)
+      (update 0 binary-to-num)))
+
+(defn take-literal-value [packet]
+  (let [[tid data] (split-at 3 packet)]
+    (when (= '(\1 \0 \0) tid)
+      (let [sd   (into [] data)
+            spl  (split-with #(= \1 (first %)) (partition 5 sd))
+            nums (map rest (concat (first spl) (take 1 (second spl))))]
+        [(binary-to-num (reduce concat nums))
+         (drop (* 5 (inc (count (first spl)))) sd)]
+        ))))
+
+(defn take-operator [packet]
+  (let [id (first packet) ps (str/join (rest packet))]
+    (if (= \0 id)
+      (let [bits (binary-to-num (subs ps 0 15))]
+        [(subs ps 15) bits :bits])
+      (let [pkts (binary-to-num (subs ps 0 11))]
+        [(subs ps 11) pkts :pkts]))))
+
+(defn process-packet [[input vcnt]]
+  (let [[version data] (take-packet-version input)]
+    (if (every? #(= \0 %) data)
+      ['() vcnt]
+      (do
+        (if-let [value (take-literal-value data)]
+          [(second value) (+ vcnt version)]
+          (do
+            (let [info (take-operator (drop 3 data))]
+              (if (= :bits (get info 2))
+                (loop [inpt [(subs (first info) 0 (get info 1)) (+ vcnt version)]]
+                  (if (empty? (first inpt))
+                    [(subs (first info) (get info 1)) (second inpt)]
+                    (recur (process-packet inpt))))
+                (loop [n (get info 1) inpt [(get info 0) (+ vcnt version)]]
+                  (if (pos? n)
+                    (recur (dec n) (process-packet inpt))
+                    inpt))))))))))
+
+(loop [packet (->> (slurp "./in")
+                   (map hex-lookup)
+                   (take-while some?)
+                   (reduce concat)
+                   (str/join)
+                   (#(vector % 0))
+                   (process-packet))]
+  (if (not (empty? (first packet)))
+    (recur (process-packet packet))
+    (println (second packet))))
+