day 4, part 2

src/day04.clj

@@ -8,23 +8,48 @@
 
 (defn parse-line [l]
   (let [m (rest (re-find #"Card +(\d+): +([\d ]+) \| +([\d ]+)" l))]
-    [(read-string (first m)) (mapv parse-numbers (rest m))]))
+    [(read-string (first m))
+     (assoc
+      (zipmap [:winning :had] (mapv parse-numbers (rest m)))
+      :copies 0)]))
 
 (def input
   (->> "inputs/day04"
        slurp string/split-lines
        (mapcat parse-line)
-       (apply hash-map)))
+       (apply sorted-map)))
 
-(defn count-winning [[_ [winning had]]]
+(defn count-winning [{:keys [winning had]}]
   (->> (map #(some #{%} winning) had)
        (remove nil?)
        count))
 
 (def part1-answer
-  (->> (map count-winning input)
+  (->> (vals input)
+       (map count-winning)
        (map #(case %
                0 0
                1 1
                (pow 2 (dec %))))
        (reduce +)))
+
+(def part2-answer
+  (->>
+   (loop [cards input
+          todo input]
+     (if (empty? todo)
+       cards
+       (let [current (first todo)
+             current-id (key current)
+             current-copies (inc (:copies (val current)))
+             matching (count-winning (val current))
+             to-win (range (inc current-id)
+                           (inc (+ current-id matching)))
+             cards' (reduce
+                     (fn [cards i]
+                       (update-in cards [i :copies] (partial + current-copies)))
+                     cards
+                     to-win)]
+         (recur cards' (drop current-id cards')))))
+   (map #(inc (get (val %) :copies)))
+   (reduce +)))