1 files changed, 66 insertions, 0 deletions
diff --git a/year2021/day8/part2.clj b/year2021/day8/part2.clj
new file mode 100644
index 0000000..1ee3c08
--- /dev/null
+++ b/year2021/day8/part2.clj
@@ -0,0 +1,66 @@
+(require '[clojure.string :as str])
+(require '[clojure.set :as set])
+
+(defn find-match
+  "
+  Searches for digit that `has segs-left` segments remaining
+  after the segments of `dig-to-cmp` are removed from the
+  digits in `cnts` with `grp-to-cmp` segments.
+  "
+  [segs-left dig-to-cmp cnts grp-to-cmp]
+  (as-> cnts $
+    (filterv #(= (first %) grp-to-cmp) $)
+    (filterv
+      #(-> (second %)
+           (str/replace (re-pattern (str/join ["[" dig-to-cmp "]"])) "")
+           (count)
+           (= segs-left)
+           )
+      $
+      )
+    (get-in $ [0 1])
+    )
+  )
+
+(defn determine-digits [line]
+  (let [counts (mapv #(do [(count %) %]) (take 10 line))
+        mcounts (into {} counts)]
+    (as-> {} $
+        (assoc $ 1 (mcounts 2)
+                 4 (mcounts 4)
+                 7 (mcounts 3)
+                 8 (mcounts 7)
+                 )
+        (assoc $ 3 (find-match 2 ($ 7) counts 5)
+                 6 (find-match 4 ($ 7) counts 6)
+                 2 (find-match 3 ($ 4) counts 5)
+                 9 (find-match 2 ($ 4) counts 6)
+                 )
+        (assoc $ 5 (find-match 2 ($ 2) counts 5))
+        (assoc $ 0 (find-match 2 ($ 5) counts 6))
+        )
+    )
+  )
+
+(println
+  (reduce
+    (fn [sum input]
+      (let [line (as-> input $
+                   (str/split $ #" ")
+                   (mapv (comp str/join sort) $)
+                   )
+            number (subvec line 11 15)
+            decoder (set/map-invert (determine-digits line))]
+        (->> number
+             (map (comp str decoder))
+             (str/join)
+             (#(Integer/parseInt %))
+             (+ sum)
+             )
+        )
+      )
+    0
+    (str/split-lines (slurp "./in"))
+    )
+  )
+